BOMB ASPECTS OP THE BIOLOGY, QV

VSHEBUPIS ITOAgPH*. (MOHTAPP ).

toy D. B. QaavXe.

T t i m l T ext

Presented to the University of Glasgow as a thesis for the degree of Ph* D* Mtiy. 19U8. ProQuest Number: 13849331

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ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 T ffik . # Qw&aa&M- 1. Introduction. Pag* 1 . 2 . AdauMrledgraent a . " 2. 3 . larva# t The Ident IfloatIon of the Vellgar# a# The problem* Page 3# b# The veliger* * #* 2# Fluctuation* in Abundance and Vertical Distribution of the Veliger* a# The problem* Page 13* b* Seasonal fluctuations in abundance* * 16* o* Vertical distribution* " 19# d# Diurnal movements* n % fetamorphoals of the Larva* a* The prdblem Page 28* b* The anatomy of the vellger* Page 30* o* The apet* " 38* d* The anatomy of the spat* w 39* 9* The Spat# a* The spatting on plane surfaces* Page 56* b* Mortality of the spat* * 8 l* «• Spasming# a# Sate of eater propulsion* Page 72* b . Shell movements* " 99* c* Spanning* " t07* d* Seasonal gonad changes. " fid* Growth* a* The problem Page 127* b# Growth in th e young* M 131* o# Growth in the adult* n 435* a. Sunsnary* Page 1i|S* 9. Seferenoea* Page 153* 10. a* Appendix 1 t Water propulsion data* b* Appendix 2 $ Growth data* c* Appendix 3 * Digging movements. Introdoctlon. The original plan in this Investigation was to study the general biology of Venerupls pullastre (Montagu) • It was soon realised that the work would hare to be confined to certain phases of the life history and these were chosen in an effort to cover the sect ions in which the information on marine Lamellibranchla. such as *QB fol* f« be inadequate* As a result, the work viewed as a whole may lack continuity and coherence* In the main* the investigation centres on the larval and spat stages of the life history; a part which feu boon largely neglected in LoraelllbrRnchia other than oysters* The efforts of Thor son, culminating in his extensive report (Thorson 192*6} on the reproduction and larval development of Danish marine bottom invertebrates, have assisted greatly in correlating and furthering work in this field* In a d d itio n to th e la rv a l and spat work, some emphasis has been placed on breeding, and while the results from this work are in no way conducive, they may be of interest in a comparative way. According to Winckworth (personal eommunicat.ion 191*8), until recent years the genus Venerupls has been grouped with Panhia and Tapes into one genus, sometimes called Tapes and sometimes by the older name Papilla* Winckworth recommends Thiele* s (1935) arrangement in which, for the species being studied here, the name Venerupls pullastra (Montagu) ie recognised* In addition the species 2* /species w ill occasionally be referred to by tbs name "oloaf , end D’Arcy Thompson (I9h7» p*288) is cited as the authority, although the name is used extensively in fltorth America*

The author is Indebted to Professor C*M* Yonge, Ph.D., D.Sc*, F*R*S», for providing faeilities to carry out this work and for hie constant help and encouragement* Grateful acknowledgment is also due to Dr* H*F* Steedfoan, and o th e r raenber© o f th e s ta f f o f th e Department of Zoology* Appreciation is expressed to Mr. R. Elmhirst, Director of the Karine Station, M illport, and to meabers of his staff for assistance in many ways* 3. fhg, V eU g tt* The literature on the ident ificat ion of the veliger larvae of lamellibrenchs le not extensive* Stafford (1942) was one of the first to do important work on th e subject* He in d ic a te d s u ita b le methods o f in v e s ti­ gation and figures, and describes eight Canadian Atlantic species* Ohdner (191U) has identified several species from Rovigno and his figures for Saxicava and Li pa are good* Readier ( 1926 ) in one of the better papers on the subject, described several North Sea speoies and his figures are clear and accurate* Lebour (1937* 1938a* 1*3») did extensive work on lamellibranch larvae and has d escrib ed 17 species from Plymouth* Unfortunately, both the figures and the descriptions are vogue and are conse­ quently of limited use. Miyazaki (1935* 1936a, 1936b) has given useful descriptions of 8 species of Japanese lamellibrench veliger s. Werner (1939) in an excellent paper, goes into the problem in detail and studies shell structure of the veliger and uses hinge teeth and ligaments as diagnostic features* He also found the erstwhile prodlesocoach could be divided into a first and a second prodissoconch on the basis of shell development and structure* The size of the first prodiseoconch, designated as Prod* 1 * is relatively constant for any given species and is apparent­ ly a more reliable diagnostic feature than Prod* 1 1 , th e v setting size of the larva, which several authors have found to vary between wide limits; although Labour (1938b) has /

set up a key for the identification of the various specie 9/ In /epee lee of Car&iura found at Plymouth* on the basis of moh measurements* Jorgensen, (19M>) describes and figures about 25 species of veligers from Banish waters sad on the whole this is a most useful work* The larvae of all commercial speoies of oysters haws been figured many times and these are prcfeably the best known of all marine lame 111- branoh veligers. A fact to be taken into consideration when des­ cribing lamellibranoh veliger 8 is that those who ere apt to make most use of the Identifications are the oceanographic plankton workers* whose material is usually preserved* The colour goes quickly and all that is left is the outline* its shape and else* and the hinge teeth and ligament* All this is present only if the material has not been t_oo well preserved for even neutral formalin^ in time becomes acid and dissolves f away the fragile shells* Colour, then, often a valuable aid in identification* is lost to the plankton research worker* as are other anatomical details such as the position of the digestive gland* and the presence or absence of eye- spot s or flagella* Therefore in the description to be given fear the larva of V. pullestra, attention will be directed to those diagnostic features remaining after fixation* The essential part of a description of a veliger Is the illustration* Ho amount of written description can take its place* Brewings of the complete animal will be given as well as the external j view of a single valve* Being the whole veliger* the tilt/ j i

.j / t u t doe to the lift of the uafeonal region may vary a good deal# eo affect log the outline* The only cone i stent chape le Obtained from an external Tier of e single valve* Most authors on veliger Identification have relied entirely on camera lucida drawings} In addition to these it le believed that photomicrograph of the veliger will In the future be used to a greater extent* No phot omi orographic apparatus was available for the present investigation, eo the author*s own 35 am* camera was adapted for the purpose, end ell the photomicrographs in the thesis have been taken with the adaptation* The results are not as good as they might be, because of the difficulty in obtaining the correct focus* However, the photographs give much better represen­ tations of the larvae than the camera lucida drawings; and Hr* C*B* Rees of the Leith Laboratory of the Hull Oceano­ graphic Department, who has been studying lamelllbranch larvae from plankton recorder records, has found them to be of more value than drawings*

Method* There are two main approaches to the study of lamelllbranch veligers from the point of view of identifica­ tion* The first is to study the succession of sizes of various forms as they appear and develop in the plankton and then associate the largest of these larvae with the newly settled spat* Xn turn, the spat are followed through individuals or groups of gradually increasing size until specific identification is possible* Peculiarly enough,/ /enough, it is the identification of the spat that is often mare difficult than the linking up of larva and spat* To Obtain the spat, cardboard egg separators dipped in a maxture of tar and pitch, separated by sheila of Octree * and strung on wire, were used* The cardboard soon became coated with algee^ detritus, and the normal sequence of fouling organisms, the whole of which provides an ideal settling surface for many species of l&mslllbranehs* In addition, sand and mud from the habitats of likely species may be sieved and ellutriated* The second approach to the identification problem is to culture the larvae, either from the fertilised eggs or by picking out numbers of any one species, and attempting to culture these throu^i to the spat stage* Both these methods were used, but the letter one was more successful end easier* Culture from the fertilized egg after natural spawning by the female may be carried out, but this was not always possible* The veligers picked out of the plankton tops kept in 2 litre l&rs stirred by the plunger system* They were fed with cultures of naked flagellates, but it was found that unfed veligers grew and astamorph osd as well as those which were fed* Groups with ©and or mud in the plunger Jar were no more successful than those without* There was no consistency about any of the culture results. Some species, among which J* oullastra was fortunately in­ cluded, were more easily cultured than others* Plankton tows with fine mesh nets vers taken at frequent intervals throughout the simmer, from Xeppel Pier* The ebb tide runs southward at a rate of 3-h knots pest the pier, so that on normal tides the plankton nets fish well from the pier end the use of a boat is unnecessary# The tews were purely qualitative in nature* The laraelllbranbh larvae from the tow-netting were settled out by gravity, taken by pipette to a watch glass, and by gentle hand centrifuging, separated from the remainder of the plankton# The material was always examined in the fresh condition for useful identification characteristics are lost on preserva­ tion* At first, earners lucida drawings were made of each stage of each new species as It entered the plankton# Later, the caraera lucida was replaced by the camera, and now a library of several hundred negatives is available for reference purposes* At first it was necessary to study the whole plankton in order to isolate X* uullastra# but after this was identified. Interest was maintained in other species, a final total of 17 being identified of which five are new# Three of these are specific, the other two still generic* There are a nurfber of standard features which may be used in identification of lamelllbranch veligers, but often in the last analysis, due no doubt to the fact that many sp ecies vary go little from one another, the general impression, a composite picture of all details, is probably the most important* Some of these characteristics are 8 - 1 . General outline or shape* The wedge shape of yft«a hi ana illustrates this well* Its shape Is unique amongst larvae hitherto described* 2* Colours Usually only useful in fresh material* although the deep yellow of the ventral shell area of J[. pullaatps* way persist for some time after being preserved* The odour of the digestive gland is often & useful cheracteristiot that of Telling tenuis is green* while ftjffilftW M gfcte is brown# J* Shape» prominence and position of usfcooasx The shape end prominence of the unbones is best illustrated In the oysters* The incubatory (lerviparoue) species have large, broad* round umbones* while the "oviparous* species have long narrow* pointed and slightly hooked unhones. Of an equlvalve species the relatively short * email and centrally placed udbones of Teredo are most charaeteristic* h* Rqulvelve or inequivalve: Readily distinguishable* The larva is similar to the larva in this reepect* Pet res larvee are inequivalve and cullsstrs is equivalve* 5* Presence or absence of eye spots: The Anisooaysria nearly all have black eyespots* Lima is an exception* goals has a brilliant red spot under the posterior adductor muscle* 6 * Special features: Few have been found. The cleft in the ventral area of the right valve (aalage of the byssel notch) of Heteranomia is an example* % 7* Dimension end shape of Prod*t end Prod*H: These are guides, but within lim its, because they te n d to be somewhat v aria b le* 8 * Number, shape end position of hinge, teeth: Host species of the Anlsorryaria have larvae with taxodont teeth, although they may occur in other groups* The large teeth of Zlrnhaea* two on one valve and three on the other are characteristic* Of all these points, the most inmortant appear to be the general outline or shape and the hinge differences, especially with preserved material* The other character­ istics are useful for original identification work*

The larra ocf V. pal la at r a. Throughout the eumror of 191+6 samples of send from various beaches were sieved and ellutrlated and the spat picked out* At the earns time, cardboard collectors from strings of cult oh that had been hung from a raft near the Marine Station, were removed at intervals* From these* samples of the settled spot were picked off, end these collectors proved a better source of meter lei than the sand* An examination on June 12th produced about 30 spat from a square foot of surface, indicating that spawning had occurred some time before and that larvae should be present in plankton* Fortunately, previous experience with spat of various species enabled immediate identification of the earliest spat of £* pullaetra. From the shape of/ 1 9 . /« r Proa. it on tfes Tsyy young spsty in s^lition to it# mean len g th o f 260 u. * associativa « s made with a reXIgor of similar shape and size in the plankton* Further study of large veligers and young spat strengthened the opinion that this was the veliger of J£* laillaatre* Attempts sere immediately raade to culture the larvae by picking them out of the plankton and placing them in plunger jars. They s e re fed w ith a m ixture of ChlmaydomanaB and an unknown tt~flagellate from the stock cultures of the Millport Station* These food species were cultured both in 2fiqusl9s solution and in Mrdschreiber’s mixture* A email auber of the leyvae survived and metamorphosed into easily recognised spat* thus proving the correctness of the identification* Many cultures of these larvae were started* both in 19i#6 and in the suimasr of t 9 h?» with very variable success* From one culture* 5 ?T larvae metaaaorphosed into spat* of which 1*3 or were of aboonaal shape* Other attempts were made to culture them in plankton cages mads of bolting silk and susittoded from a raft* Ifo spat were ever found in these despite repeated attempts*

Description of the Lanre. The earliest larval stage definitely recognised a8 ?* pullastra was in the late straight hinge condition, iCB u. longe mad ik k u. high (Pl*1 * f ig*l) • The ventral shell area is light yellow but becomes much deeper in older larvae* The ends are well rounded and the straight hinge is placed somewhat to the posterior* thus causing th e / /the anterior margin to fall sway more rapidly than ilia anterior* Fl* 1 » f i g *2 shows an early us&o stage# 20b u* long and ISO u*high* Sera the veliger la beginning to asBwm the typical shape* generally rounded# slightly mare pointed to the anterior and deep in relation to the length* The anterior and posterior dorsal margins are slightly convex* The ventral murgla is yellow und the colour extends further to the anterior than the posterior# The digestive gland is apparent at this stage and is also yellowish* The remainder of the unlml is colourless* Xn Pl*t * flg*3 is shown a (nature larva# 260 u* long and 2k0 vu high* The ventral margin and the centrally pieced digestive gland have the characteristic yellow colour# There ©re three to four gill plates and the statocyst is plainly visible through them* The umbones in most positions in which the larvae ere seen# merge with the general outline o f the shell* In Pl*1 , flg.b is shown the interior view of the left valve of a larva 256 u. by 238 u* The length of Prod*t in this specimen was 108 u* Xn Pl.t# figs* 5 end € arc shown the hinge areas ( internal Vlas') of e larva 227 u« by 209 u* F ig . 5 shows the right and fig . 6 the left, valve# The ligament (L) is at the posterior end of the hinge# Xn Pl#2» fig#7 is shown a photomicrograph of a setting veliger# and fig #8 is a photograph of external vlewe of single valves* Fl#2* fig#9# shows an internal view of the hinge of a setting veliger and the teeth and the ligament are evident# PI.2, fig* 10* shows a newly settled spat wltV 12* /w ith iust a tree© of the diesoconch showing. The older sp at In PI* 2 , fig * 10 la 0 *h mm* In length, in which the shape, especially the anterior end, has changed from that of the larva. In © nuiber of species it hae been observed that the outline of the larval shell changes with the growth of th e spat* The prodissoconch becomes nearly surrounded by the solid spat shell, and doubtless the pressures set up on all sides of the fragile larval shell causes the distortion* Care must he taken in using the outline of the larval shell on spat for making the link-up between them, and only newly settled specimens should be used*

‘4ft ■* -T£V*fc 13. F lu c tu a tio n s in ATaumtenoa wad Vertical Distribution of the Veliger. The only lamelllbranch veliger upon which any quantitative work has been done is the oyster, partly no dotfct because of its economic importance and partly because it is one of the veligers that has been long identified and Is easily recognisable, even in the young stages* Zn some ways the oyster veliger presents a special problem in that it is most often found in sheltered and enclosed waters; at any rat© it is in this type of water that it has been most thoroughly stu d ie d q u a n tita tiv e ly * The summer o f 19W> was occupied in identifying the veliger of £• oulleetra and in becoming familiar with it* In the summer of 191*7 a pump that could be adapted for the quantitative studies of plankton became available* The work was essentially preliminary but it has revealed some of the problems*

Method* The pump used was a centrifugal ex-N.F. 8 . machine powered by an 8 H.P. Standard Qwyxme en gin e that had been used by the Marine Station plankton team for plankton work in Loch Striven* The apparatus was light enough to be loaded and unloaded from a forty foot boat without undue difficulty* The pump was initially placed on Keppel Pier and the sagging done by pumping water fro® 2 feet below the surface through a Ho* 120 bolting silk plankton net into measuring tanks of 333 litres capacity* At first, one cubic/ 14* /cubic metre was used but later increased to two* The contents of the net were washed into a large jar and the volume reduced by siphoning off excess water with a thistle funnel covered with bolting silk# The whole sample was then examined in e counting cell, in the fresh condition whenever possible, for identification is then easier and more certain* For sampling from depths greater than 15 metres, a diameter, instead of the usual 4”» Intake hose was used* This thinner hose had the disadvantage that with its use it required 15 minutes to pump a cubic metre, due to the friction. Sampling began on gone 26th, the day after the first veligers were observed in the plankton* On August 6 th, owing to the pump being required for other purposes, the sailin g station was moved from Keppel Pier to a point in a small bay to the north-east of Keppel Point# The poop was located on the shore above high water mark and the intake pipe was led down over the rocks and the intake end# two feet below the su rface, m e floated on a buoy# (P1.23, fig * 2 ). At high tid e th e intake was 12 to 15 yards off shore, but at low tide, only ©bout 2 yards# This was not th e most su ita b le position, but under the circumstances, there was no alternative. Some luforcaation was certainly obtained of the larval movements in a bay which is typical of the Island of Cunbrae, and in no way unnatural* 15* C urrents* The currents ere known to exert a great influence on the movements of larvae, and Tait (1957) has found an eddy which nearly overlies the area on the Dogger Bank of the Horth Sea, where Davis (1923) found and carefully mapped out areas of bottom containing huge populations of Bnlsula and Mactra* These areas appear like islands with definite borders and are indicative that some agency like a current must have been responsible for thus concentrating the larvae# Orton (1937) in a study of the spatfalls of Cardiua ednle in Borecambc Bay, found that the heaviest spatfalls occur where (a) tidal streams meet, and (b) share banks shelter a stretch of ground from prevailing winds# The current configurations in the region of the Curcferee are not well known and the work of Mill (1892, 1894) gives little information on email local areas# However, observations during the sampling period, as well as at other times, gave acme indications of the surface picture# On the early part of a flood tide the flow of water comes in across the mouth of Karnes Bay (see Plate 3# Map) from between the Ounbraes; it strikes Farland Point and is deflected to the southward across to Hunt erst on Perch* As flooding proceeds, the direction of the current backs end flows more directly up Fairlle Channel and In time swings far enough to be deflected by Keppel Point* First to the last, end later to the Horth of this stream, there occurs a reverse eddy or swirl# E a rly/ 16# /Karly In the tide it affects the whole shore betw een th e Lien Hock end Keppel Point; later it is confined to the email bay between Keppel Pier and Keppel Point* This is a rough picture of the average surface current conditions on the flood tide in this area, but many variations occur. The ebb stream is more straightforward and for a period during each ebb, the tide will flow strongly southward pest Keppel Pier where it Is often used for fishing plankton nets. At no time, however, in spite of the rate at which it strikes Keppel Pier, doe© it hit the north-east shore of Keppel Point with any force and the surface current past the Intake of the plankton pump, was not observed to exceed an estimated $ to f knots.

Seasonal Fluctuations in Abundance of Larvae* To determine fluctuations in abundance of larvae throughout the summer, samples were taken os nearly as possible every four days during the period when veligers were present in the plankton# The results from June 26th when th e f ir s t larvae appeared, to September 30th when they disappeared, are shown in the graph,Piste 4* Included are the average weekly temperatures taken at the surface from Keppel Pier. These temperatures were kindly supplied by Mr. K*A. P y eflneh, B.I.S.B.A#, Millport. Practically all larvae represented in the graph range from 180 to 260 u* in length# For some unknown reason the younger stages did not appear to be represented in either the qualitative or quantitative samples in adequate numbers comparable to the/ 17* /the frequency of the older stages. This precluded the possibility of obtaining slse~frequeney distributions from whleh it may have been possible to make on estimate of the length of larval, life* The first larvae noted on June 24th were at least 160 u. in length, showing they were about half grown. If the drop in the frequency curve on July 12th indicates the disappearance of this initial population due to settle­ ment, the duration of larval life la approximately 50 days# T his i s not im probable, e s p e c ia lly when tb® tem peratures are considered*. Thorsoa (1946) gives figures of k wo ska f»* Jdailfl and 2 neks for gas SE£B2£l£- H«l»oa (1928) considers the larval life of Mytllua adults to be three weeks and the same time far Mys erenarla ot tempera­ tures under 20° 0* Weymouth, McMillan and Holmes (1925) believe the larval life of the razor clam, Bilious, is about two months, but that it is not free swimming during all this time. Field (1922) estimated a larval period of two months for Mytllus edulis by comparing reared larvae with those found in nature. The duration of larval life Indicated by laboratory cultures fluctuate greatly according to the author's experience with V. nttllaatrc. Octree glgce (Elsey, 1933) requires about 3 weeks at temperatures between 18 end 20° C. Schaeffer (1938), found that the larvae of £♦ gjgas took 3 t o 6 weeks depending on temperature, to reach setting sise in Quilcene Bay. Surface temperatures v aried betw een16 and 23° C. Hopkins (1937) states that/ 18* /that the larvae of £, lurida have a free swimming period of a month after being released from th© brood d ialer. O rton (1937) estim a tes th e f r e e swimming p erio d of £* adults to be 10 to 14 days, and various other authors, Cole (1936, 1939), Maszorelli ( 1922 ), Hagneier (1916) and Srdman (1934), find the times to vary between 9 and 17 days depending on the temperature within the range 15*0 to 22*0° C* Assuming a larval life of 30 days for 2* anils stra the date of the first spawning would be about June 10th and th e m m weekly temperature at this time (Keppel Pier) was 9,|® C, One female has been observed to spawn in the laboratory at 10° C* but that is the exception rather than the rule; the majority require a minimum temperature of about 16° C* June 23rd~28th was the first 5-day period in 1947 that the surface temperature at K©x>pel Pier rose above 10° C« It must be remembered that animals on the beaches may be subject to higher temperatures, and on a sunny day during the time of spring tides, the temperature of the incoming tide over the beech may be at least 5° h ig h e r than the temperature recorded at Keppel Pier* The group forming the peak number on August 23rd would have spawned approximately 2 weeks earlier, which would coincide with the increase in temperature beginning about August 10th. This is largely conjectural, and a more satisfactory sampling station, with an extensive study/ 19 * /study of the Xength-froqueney of the larvae, would verify these assumptions* One point that te elicited from the data is the exect period of the breeding season* Xn 1946 spawning began before June 1st, for the larva© were first identified in th e f i r s t week o f th a t month* On June 12th a nuniber of newly settled spat were found and this indicated, assuming a free swiwniag period of a month, that spawning had eoourred Mb out the middle of May# The tt^ e v v tw r e in «td-4fey, 1946 wee only 8*5° C* at Keppel Pier, not rising above 10° C* until the first, week in June* Xn 1946 the larvae disappeared from the plankton in the middle of August * Thus in 1946 the spawning season lasted from mid-May to mid-July, assuming a larval period of a month. Xn 1947 the season was from mid- June to the end of August* Spawning in two sueoeeeive years la s te d f o r about th e same le n g th of tim e , but i t commenced a full month lata* in 1947* This lag tasy have been due to the retardation in gonad development subsequent to the exceptionally low winter temperatures in 1946-47* It is usually in the pre-spawning period that the intense pro­ liferation and ripening of the laollusean gonad takes place*

Vertical Distribution. Thereon (19V>) and Barker Jorgensen (192|£) have . provided the only information on the vert leal distribution o f lame 11 lbranoh veligers, other than oysters# Xn the 8 ound, however, the distribution la markedly influenced by/ 20# /bgr the layering of the so-called Kattegat and Baltle w a te rs, and the data from those works have only lim ited application* It was hoped to determine the normal vertical distribution of the larvae of 2 * ou^lastra and to oorrelate this with the vertical distribution of the settled spat* To collect information about epatfell, a nuttfber of strings of cultch were suspended from surfaoe to bottom, in various depths, down to 40 metres, in several localities* Extreme care was used in the preparation of this experiment; only new rope, with new galvanised thimbles and shackles, and special anchors and buoys were used? however, every string was lost and in the opinion of the Station boatman, vandal­ ism was the cause* To obtain a general picture of the distribution of larvae, surface samples were taken on July 29th at 4 stations - Balloeh Bay, Huntereton Perch, Trail Island and Keppel Point* Larvae of 2 - oullastra were found only from Keppel Point, where 20 were counted* This trip coincided with a period when the population was low, as indicated by the counts from the regular series of samples (Graph, Plate 4) *! It is significant that this evidence corroborated the infor­ mation from the regular series* A station was later set up in F alrlle Channel (Plate 3, P) * and samples of one cubic . metre were taken from depths of 3 , 9 , 15, 25 and 30 m etres* A period of 9§ minutes elapsed between the first end last sample of this series* The results are summarised below* T ab le

YffWPigfo Vertiool Dletrlbutlaa of Larvae <11 fftrHMI?- < oublc mot re wmplo*.

Tims Depth Ho. of Remarks. In m etres L arvae

13*25 3 0 Few lam elllb ran ch v e lig e r s . 13*10 5 1 Horrael surface larvae present* 13*00 15 6 Considerable number of normal surface forms* 12.35 25 0 Smell no* of M ytllua ed u lls* 12*15 30 1 A no. o f J|« edulls* 1 Modlolttf modlolm. _ No o th er 1 smelllbreneha. W eather i Calm during the surface samples* Slight chop during the vertical series*

These nunbers are too email for much significance to bo attached to them* nevertheless* they indicate that tbo larvae of J. pollastra do penetrate below the surface lifers and the small numbers found agree with the result a of the regular surface aeries* A second vertical aeries was taken at a station placed aa nearly as possible to the position of the July 2 9 t h station* (Plate 3* F)* Sampling was done in the same manner but from the depths of 0 9 5 * 1 0 * 15* 2 0 * 2 5 * 5 0 * bO and metres* a volume o f 2 cubic metres was used for each s a m p le and a period of 7 hours elapsed between the first end the/ 2S» /the last sample* Hie results are euasi&rlsed below and graphed on P la te 5 *

T able 2*

Vortical PlgtrlbTrtloa Qf Lax^»«a* ln in Palrll!Pairlla Channel 2 otfcic nwtra sample..gjj.g.fr?'

T in s Depth Ho* o f Remarks. in m etres Larvae*

10 . 1a 0 26 Few oth er v e lig e r s * 10*30 3 30 Formal complement of surface forms* to .5 3 5 32 Fair no. of other veligers* 11*20 10 97 50$ of veligers were ¥• oullas- JUDd4 11*56 15 67 Normal complement of veligers* 12*30 20 5fc Formal complement of veligers* 15*20 25 15 Formal complement of veligers. 16*00 30 26 Formal complement of veligers* 16*50 w> 0 Few veligers. Mytilus edulls and Modiolus modiolus* 17*10 0 91 V elig ew m ainly 2. onllaatra.

Weather i Calm and sunny.

Owing to the long period of time Mween samples* comparisons between numbers at different depths hare little signifieanee* ^he information does indicate that £* pullaetre and other veliger larvae may be found over By /e considerable range of depth* It la not known whether the behaviour of the larvae la responsible for this or whether the Observed distribution is the result of a fairly . complex tidal system at this station. Thor son (19M>) , found that larvae were confined to their * 0811 x 0* w ate r, characterised by a certain salinity and teosperature; and Kelson (1928) found that the larvae of £• vlrglnice congregate at the hallcllne In Barnegat Bay. Ko hydro­ graphic estimations were made, but there is little evidence for the existence of a definite hallcllne In a tideway such as Fair lie Channel* Perkins (1931) , also working In Barnegat Bay, found a possible correlation between the vertical distribution of the larvae £* vlrginica and the and the strength of the current, although at low current velocities and marked salinity variations, this latter factor appeared to effect the distribution as found by Kelson* The Interpretation (Korringa 19hO) of Perkin* s data is that the effect of salinity changes is greater than that of current velocities* Working In the Costerschelde, Korringa found the larvae of £. edjulls were uniformly distributed In a vertical plane at any time of the day or night. In aU kinds of weather, and at all stages of the tide. It nay be pointed out that the water in the Oosterschelde la shallow* i 24* Diurnal Movements. Oa August 1Uth* 15th anfl 16th, 19U7> «anple» o f 2 cubic m etres were pumped a t each low , h a lf and h ig h tide period from the Keppel Point shore station (P1.3# Bap 0), giving a series o f 16 samples over 48 hours* Besuita of the larval counts for these samples are tab­ ulated In fable 3* *nd shown graphically on Plate 6 * This Shows that the number of larvae is closely correlate with the stage of the tide and also, to some extent, with the periods of darkness# In order to check this data and, If possible, to eliminate the possible effect of local conditions such as the eddy factor and the proximity of the intake to the shore, a series of samples were token from the 'Nautilus 9 during the period 26th~28th August 1947» at a station (Fl*3t D) 200 yards south of Keppel Pier In l|0 metres* These samples of 2 cubic metres volume were taken, as before, approximately every three hours, coinciding with the times of high and low water and the half tides* In addition to the surface sample, one was taken near the bottom a t 12 metres* It required 13 minutes to take each sample* The results of this aeries are tabulated In Table 4 and graphed in Plate 7* The direction of the surface current during the times of sampling was interesting* It appeared to occur at random and no direct correlation with the rise and fall of the tide existed* This imy be true only for this area/ Yenerupis nnllBBtr*. MRr.j£.,h#ry*$. P,

T in s Nu®&er L ight T ide o f Larvae

11.30 35 Day H 14*15 14 Day H alf 17*15 2 Day LL «MT 2 Day H a lf 23*25 30 N ight HH 02*25 69 N ight H a lf 0 5 .1 0 4 Day L 09*15 25 Day H a lf 12*15 70 Day a 15*10 11 Day H a lf 10*15 8 Day LL 21*20 120 Day H a lf 00*20 92 N ight NT 03*30 155 N ight H a lf 06*20 25 Day L 09.55 86 Day H a lf

H m High* HH m Higher High* L * Low* LL * Lower Low* Weather : Bdgfct and manny. Ho wind or aea* IS&UzJh Veneraple pglXaetrs. SAaa^LRlffilAi^iManil Metr.. aemnlee o f 2 Cuiblo feirUs-gteaflgilt Botraa. Awcuet 2fc-2ti.12h?.

BeptK fb* SP f t m la Eierreo, L ight Tide Remark* M etres 12.03 0 .6 12 Day H alf Ebb stream . 12*20 12.0 21 Bay H alf Ebb stream. Bore of other species of veliger s than in surface sample. 15.16 12*0 34 Bay Low Flood steam. Normal vellgers complement. 15.30 0 .6 11 Bay Low Almost pure culture of tin tir.nl8 Perella Btrlatuc. Only veligers, V. pullastra and Cardlma edule. 18.20 0 .6 45 Bay H alf Ebb stream - flood stream 50 yards south. Relatively few tlntinnids. Veliger content normal.

18.3* 12.0 29 Bay H alf Ebb steam - flood stream 50 yards south. Relatively few tlntinnids. Veliger content normal. 21.1(0 12*0 5 High* High Easterly chop. Few veilg en Some Crustacea and some Ceratium . 22.00 0 .6 TO Siefct High Bormal complement of vellgera. Ebb steam. 00.91 0 .6 107 B ight H alf Flood stream. Fair number of ywella. Sormal yellgen sp e ele s. 01.0J 12*0 1 B ight H alf Few vellgers - mainly Slfctella end Heteranorala. 03.51 12*0 11 B ight Bov Flood stream. Normal

0U»H 0 .6 77 B ight Low Flood stream. Formal complement. /O ver i Depth 1¥ o .’ o r ~ Time in L arm t# t i g h t Tide Remarks le t* * * 07.014. 0*6 16 Day H alf Ebb stream. Ho deep s ta p le - pwap troiible* 10.33 0*6 2 Day High Flood stream* Few plank- tore of any sort* 10.1*3 12*0 25 Bey S ig h Hortnal plankton. 13.30 0 .6 5 Day H air Ebb stream, L ittle plankton Few M yillus. 13*45 12*0 50 Day H alf Hormal veliger complement* 16*30 0*6 7 Day tow Changing from Ebb to Flood stream* L ittle plankton of any sort* 16,30 12*0 15 Day Low normal complement* 13.50 0*6 47 Day H alf Flood stream . Few o th e r veliger apeolee* 20*05 12*0 56 Day H alf normal complement* 22,1*5 0*6 105 E ight High Flood stream* Vellgere normal* 23*00 12*0 20 n ig h t High Changing to Ebb stream* Vellgers normal* 01*53 0*6 206 H irh t H alf Ebb stream* Vellgere normal* 02*13 12*0 0 S ig h t H alf Pew vellgere* 05*00 0*6 20 Day Low Slack water* 05*20 12*0 34 Day Low Beginning of flood at ream* 08*25 0*6 34 Day H alf Ebb stream, normal vellgeri 08*40 12*0 33 Day H alf Slight ebb* Many esmstaeeas Veilgars of larger else groapa. Hvtilaa dominant* 11*27 0*6 i f Day High Light flood* 11*45 12*0 14 Day High Slight ebb* Few vellgere* 2 5 * /erea ee the station was close to the outer edge ©f the Xeppel Polat-Lion Sock swirl* Some of the samples were no doubt taken from the * swirl* water, while others were from the main current. The complexity of the surface current has been emphasised. The maximum nunbers in the surface samples coincide with the periods of darkness* In the 12 metre samples the numbers rise to e peak during the hours of daylight, but are always ranch lower than those in the surface samples. The explanation probably is that the larvae are widely distributed In depth during the day but concentrated near the surface at night, as with many plank­ ton organisms. In this series there appears to be no correlation between number of larvae and the stage of the tid e * Another series of samples was taken, again from the shore station at Keppel Point, but at less frequent intervals. The samples were most often taken at high tide with smaller numbers at low tide. Sampling was continued for five days and six nights, from August 29th to September 4th, 1947# and the counts are presented in Table 5 and graphed on Plate 8* In five out of the six night samples the numbers of larvae are significantly higher than those takes at comparable stages of the tide during the day* This corroborates the evidence from the two previous series/ T able VenoruDla pglla«tg». aw « HlghtDlBtrlbatlM or LaTTOaat^tiiftKgppel Point Short Station. August 29th to Sontonteoy hth. <9 hi.

Kudber Time of L ight T ide Remarks Larvae 12*15 9 Lay High Calm. Pew v eil gars* Si^OO 96 Hirht. High Calm* P a ir nurriber o f v ellg ere* 12*55 24 Day High Calm* Pew v elig era* 19*05 31 Day Low Calm* Large number of small vellg ere* 01*00 311 Night High Calm* Many thousands of vellgers* 07.15 Day Low Too much weed - im possible to count* 13*25 29 Day High Calm* Pew v ellg ere* 19.15 1 Day Low Calm* Pew vellgere* 01*30 378 N ight High Calm* Moonlight* Numerous v ellg ere* 08*30 42 Day Low Calm* Pair number of vellgere* 13*50 10 Day High Calm* Pew v e llg e re » m ainly ModiolwiB (aarnwrBtfi. 19.30 9 Day Low Calm* Pew vellgere* 02*00 151 N ight High Calm* Pair nunber of vellgere* 14.30 108 Day High Calm* Pair nuaber of vellgere* 02*30 17 N ight High Blight westerly* Pew vellgere* 15*15 19 Day High Cloudy.► Extremely few vellgfers* 03*30 137 N ight High Southerly breeee» rain* Numerous vellgere* /series, that these larvae undergo diurnal vert leal migrations. tn the share samples it is possible thst there raay be a diurnal horizontal movement , but this la hardly likely in view of the information from the 12*0 metre samples in the August 26th~28th series and fbom the vertical series of August 22nd in Fairlie Channel* Further evidence is needed on this point t and the present work has only pointed out a strong possibility that some sort of a diurnal rhythm exists* Further sampling is needed at more and other stations in addition to labora­ tory experiments and observations on the larvae* If a vertical migration does exist, even within the compare!Ively narrow lim its of the surface and 15 m etres, a mechanism f o r b rin g in g about th i s movement i s required. Several of the samples indicated that the migration may take place within a period of three hours* This requires a velocity of 3 metres per hour, or rou^Hy 10*0 ecu per minute* Ho data is available on the rate of awinsniog o f th ese larvae* Diurnal movements have been observed in a nuafoer of animals and Welch (1935) states, ^Diatoms, flagellates and other organisms with weak locomotion have been observed to manifest diurnal movements, but are restricted to narrow limits** Fox (1925), found that Paramecium end echinoid larvae under certain conditions swim down in light and up in darkness, and so concludes that diurnal movements occur in organisms moving by ciliary action* Kikuohi (1930),/ 2 7 . /feikuehl (1930), reviews the literature on diurnal move­ ments of plenktonic Crustacea and mentions that limited diurnal migration of diatoms, flagellates, Protases, Rotatoria and other organisms with weak locomotor activity have been observed, but that Ceratium and Anursea make more extensive movements* Re does not give his authority for the information on Ceratium and Anuraea. and this has net been found elsewhere. Rose (1925), discusses in detail the possible causes of diurnal movements. Holmes (1902), discusses phototaxis in Volvoqt which he finds is phototaotic in normal light, negatively so in Intense light, and with no reaction in weak light. Thus the literature throws little light on the possible mechanism other than ciliary activity for carrying out diurnal move* meats by £* ouflastrs* 2 8 . Metamorphosis of the Larva. The change from the free liv in g larval stage into the more or leas fixed or sedentary form in lamellibranchs is recognised as perhaps the most c r itic a l stage in th eir life history. The anatomical changes that occur in the fixed forms like the Ostreidae are more drastic than those which take place in, for instance, the active burrowing forms like the Veneridae. As well as the loss of the typically larval organs there is also the loss of the foot, of a ll or part of one adductor muscle, and a general sh ift in the symmetry of most of the organs of the attached forms. It is on these attached forms, especially the oysters, that the major part of the work on metamorphosis of larval lamellibranchs has been carried out. Ryder (1882, 1884), Jackson (1888, 1890), Stafford (1913) and Prytherch (1934) have given accounts of the process in the American oyster, Qstrea vlrginica. On the European oyster, 0. edulis, until the work of Cole (1937, 1938a, 1938 b ), there had been no adequate description of the transition stages. Yonge (1926), gave a description of the early spat, and Erdman (193b-), gave a complete descrip­ tion of the fully developed "ansatzreifen" larva. ♦ Most of the remaining studies on metamorphosis have been done on freshwater m ussels. Because of the parasitic stage in their li f e history, comparisons with marine species are not easy to make. Ziegler (1885) 02*/ 2 9 * / m Cveles cornea. Harms (1909) on the Unionidae generally and H ebers (1913) on Anodon&a c e l le a s t s * have gone in to detail on the metamorphosis of these forms. In addition, Slgerfooa (1901) on the Terediaidae and Drew (1897, 1898, 1901) on the Prot obranchia, have contributed to an under­ standing of the change from the pelagic to the benthic l i f e . The purpose of this study of the metamorphosis of larvae into the spat of J. oullastra ie to examine, in a general way, the major changes that take place during this critical period, and to sea whether they throw light on the activities and reactions of the young animals* It Is not proposed to go into the changes In much detail, for the enhryologioal and developmental studies that would be involved are beyond the seope of the present research* Xt is also necessary to limit the size of the spat examined and this has been placed at a length of 1*0 mu

■ a tta in and Method*. Plankton was taken in the ordinary way by tow matting or by pump and the larvae separated out and fixed in Bonin, which decalcified at the same time* The spat, also fixed in Benin, were obtained from plunger jars in which they had been reared from the larvae , or were taken from plates of various materials which had been exposed as eultdu Fixation was good though considerable shrinkage occurred (Orton, 1937)* Sections were cut at 7 u« in Ester/ 30* /E ster wax sad stained with methylene blue and erythroein* Whole mounts and dissect ions were stained in various ways but methylene blue was found to be satisfactory* To form © basis for following the process of metamorphosis, © description of the larval anatomy is deemed necessary. Development will not be discussed as that is another problem, and the organs to be described hers are those of the mature larva ready to metamorphose. PI.9, fig.lh is a seml-diagrararaat 1c illustration of a larva reconstructed from examination of living specimens, whole mounts and sections. The individual organs will be dismissed separately.

iag-.M s.iw j Jhum* The S h e ll. The larval shell, according to Werner (1939), is a calcified structure with a eonchyolin base, end at this stage of development, it completely encloses the body of the larva. It has the characteristic shape with the deep yellow colour, especially in the ventral region toward the edge of the shell. There are two main parts to the larval shell, an earlier formed area designated by Werner (1939) as the first prodlssoconch or Prod.1, and the part formed later, the second prodlssoconch, Prod.11* Prod*1 is of uniform surface structure with an anterior-posterior length of between 95 end 105 u* in different individuals. Prod* 11, the large outer part of the larval shell, is concentrically/ 31* /eoneentriealOy striated with fine lines. wernar* s explanation, is that Prod.1 is laid down uniformly by the shell gland, whereas Prod. 11 is laid down by the mantle edge as in the manner of the adult, and the striae ere actually growth lines. The length of ?rod.1i at the end of larval life is between 250 end 2d0 u. As far as osn be ascertained, there is little variation in shape at this time. The hinge of the larva is roughly 80 u. in length and is in the form of a solid bridge studded with 15 small teeth (?1.2, fig.9) , the centre one being bifid. At the posterior end of the row of teeth is a ligament (I.) 10 «• wide and 15 u. long. When the valves era separated ter dissection the ligament splits into two parts, one remaining with each valve.

Tbs Mantle. The mantle, one cell layer thick, is well developed and the edges are already functioning as a region of shell deposition (Werner, 1939). The lobes are separ­ ated except for a short distance near the origin of the g ills and dorsally between the adductor muscles where fusion with the visceral mass occurs. The mantle edges carry two lobes instead of the three normally fo\md in the adult (Tonga, 19h8). There are three cell layers in this region, one of whloh continues into each of these two lobes, while there is a third central one with nuclei which stain bright green with methylene blue, (P1.13, fig.26). Presumably the two lobes present are the/ 3 2 . /the inner muscular and the outer secretory# Bo nerve wee observed in the mantle lobes of the larva# On the inner side of each muscular lobe poster­ iorly below the gill origin is a line of cilia (Pl#13» flg#26c) • The cilia from the two lobes may interlock and may thus form an effective barrier to the flow of water into and out of the mantle cavity# The velum is the organ of feeding and the gills are not concerned with this in any way# The cilia of the gills ere very active indi­ cating that they may be functioning as a respiratory organ, sc doubtless there are currents in and out of the mantle cavity# It is therefore likely there is a mechanism for controlling the force and direction of these currents and for preventing the entry of particles# It is suggested that the rows of interlocking cilia in conjunction with the muscular lobe of the mantle may function as the controlling mechanisms#

G ills - The gills of the mature larva consist of four filaments# In the larva of this and most other siphonate form s, the g i l l s appear to be formed considerably in advance of those of Oetrea edulls according to the descrip­ tion given by Cole (1938)* Erdman (1934) , in his figure o f an "ansstzreifen” larva of edulia» shows only a row of six short processes representing the g ills # The gills lie in th e vertical plane between the / 33* /the posterior part of the digestive gland and the mantle edge (PI.9, fig* 14, i.g*). They are attached anteriorly la the region of the anterior foot root; dorsally by strands of muscle to the visceral mass and posteriorly to the region of mantle fusion* At this point filaments originate by vert leal splits in the block of tissue lying in that reglosu In a mature larva the longest (oldest) filament is 90 u* long and the shortest (youngest) 25 n* in the fixed condi­ tion (Plate 11, fig*17, l*g* 1-4)* The arrangement of the eille is difficult to determine at this stage, but living material shows working cilia between the filaments*

The foot of the larva occupies the postero-ventrol part of the mantle cavity, adjacent to the velum whloh lies directly in front of it (Pl.9, fig*l4f) • In the natural resting condition the sole of the foot lies parallel to the ventral margin of the mantle edge with the tip pointing forward* The posterior pedal retract or (Pl*10, fig*l6, p*r*) tuns along the heel of the foot, continues dorsal past the anterior margin of the visceral ganglion, then posteriorly over the top of the posterior adductor* At the level of the visceral ganglion it bifurcates and the branches extend on each side of the rectum to be finally inserted into the shell just above the adductor muscle* The anterior pedal retractor runs along the anterior edge of the foot eng/ 34* /and above the cerebral ganglion to bo inserted, c m branch on each valve, above the anterior adductor* The musculature of the foot is not well developed at this stage, for it is unlikely that it is used to aqy extent in the pelagic period* However, planktoni© larvae, resting on the ventral shell edges, may move along the bottom of a watch glass by the ciliary activity of the foot which is extended forward in the direction of the movement# Newly metamcrphosed la rv a e do not use t h i s method of locomotion, but exhibit feverish pedal activity in the form of the typical sequences of digging movements of the adult* The larvae of Mytllua edulls also move by means of the ciliary activity of the extended foot, and th is method of locomotion is retained in the young spat* It is remarkable that the nerve patterns of the adult are outlined so early* According to various authorities, the byssal gland is originally paired, but whatever its previous . history, in the mature larvae of JJ* nulla at ra it consists of a relatively large single sac occupying the major part of the foot (Pl*9, fig* 14* b*g*). It extend* from near the tip of the foot to the edge of the pedal ganglion* At this time there la no duct connecting the gland to the deep bysoal groove (b*gr*)* The contents of the byssal gland in the larva stain a light blue with methylene blue, quite different from the darkly staining mas* charecter­ istic of the byssal secretion in the adult* 35* Musculature* The musculature of the foot has already bean dealt with end the velar muscles will be described along with the velum, thus leaving only the adductor muscles* These occupy the same relative position they do in the adult* In some sections they appear to be divided into two parts, which may represent the "quick” and the "catch" sections, but it is not too definite* Erdroan (1934)* also raeotions that some of hie sections of Ontras edrill* larvae seem to show this division, but he does not oonmit himself further*

Digest Iyo Sygtam. The digestive system consists of a mouth situated on the posterior lip of the velum and is guarded by an oral flap (Pl*9, fig*? o*f*)* From the mouth proceeds a long oval oesophagus, 2 5 u* wide and 10 u* deep In a fixed condition, lined with long cilia* The oeso­ phagus extends along the posterior edge of the velum to the point where this joins the visceral mass, and then continues into the base of the stomach* This is a sac- like body on the roof of which lies the gastric shield* At the posterior end is a constricted portion with heavily ciliated walls, the style sac* The posterior extremity of this (Pl*9, fig* 14, k*s«), lies close to the posterior adductor and the visceral ganglion* From the posterior part of the stomach, close to its junction with the style sac, emerges the slender intestine which rises dorsally/ 36* /dorsal ly and runs in an anterior direction over the top ef the stomach* It loops to the left et the front of that organ and returns in a posterior direction high within the left- unbone* Along this ccui’se it takes several short vertical loops until it begins to descend, still close to the dorsal edge, passing between the fork of the posterior retractor muscle, with the anus just below the base of the posterior adductor* Two digestive diverticula, one on each side, ere connected to the stomach* In frontal section they are pear-shaped bodies whose pointed extremities extend to the anterior lim it of the stomach and whose single ducts open into it about the level of the visceral ganglion*

Berrora Syetwa oafl S-nae Organ*. The nervous system of the mature larva is comparatively well developed* All the ganglia found in the adult ere present as singularly large bodies of nerve tissue* The ganglia, which are paired, are complete with commissures, but the connectives, if they exist at this time, are not readily evident* The visceral ganglia ere adjacent end anterior to the posterior adductor muscle* The cerebral ganglia ere intimately connected with the apical area of the ▼dum, one ganglion lying on each side of the apical groove (Pl*10, fig* 15)* The pleural ganglia lie close to the mantle against the thin roof of the velum and ventral to/ 5 7 . /to the cerebral ganglia, to which they are linked by connectives* The pedal ganglia are situated in the root of the foot (FI* 9 and 10, fig. 14, 15, 16). Connected with the pedal ganglia are the paired siatocyets, which lie one on each side of, and above, the ganglia* Sash stutocyst contains a single statolith# Neither flic abdominal sense organ or the osphradium has been observed in the lai’v© of polls strft*

Heart. Parloardiqc) anfl Kidney. Various authors place the anlage of these organs as a group of cells close to the rectum, between the posterior part of the stomach and posterior retractor muscles* Xn these sections of adult larva, it. is impossible to point with any certainty to any group of cells as being the anlage of these organs* tn the mature larva no heart or kidney exists as such, and the essential development takes place after metemorphoele*

Velum* The velum is one organ characteristic of pelagic laaslllbrsneh larva* Xn the fully developed veliger it is the largest single organ and occupies at least 2/5the of the volume of the shell cavity* When extruded, it is circular and about 180 u* in disaster and appears to be dilated along its whole margin* The long peripheral cilia are roughly 50 u* in length and the shorter about 10 u* Tit® m argin o f the velum is a thick heavy structure of cuboids! epithelium, which folds and creases whan the velum is retracted (KU9, fig* 14, v«l«)« Xn the centra of the roof of the velum is located the cone- shaped apical plate, which stains deeply with methylene blue* Xn its centre is a groove (Pl*10, fig*1$, *»P» a.g*) in the plane of the dorso-ventral axis of tbs body* There arc* anterior and posterior pairs of velsr retractor muscles, the 1st tor are inserted in the afceh of the shell anterior to the hinge ligament, and the former on the bulge of the valves posterior to the anterior adductor* The single at rands of the velar muscles branch at the ends to give multiple insertions on the valves and on the velum*

The S pat* The spatting or settling act in non-sedentary forms like X* ^ullaa^re is not so defined as it is in cementing forme* Three of the most important and readily evident changes that may be taken as Indications of meta­ morphosis are s 1. The loss of the velumj 2* The functioning of the byssal gland; and 3* The formation o f th e sp at s h e ll or disBOConch* The immediate loss of the velum in oullaatra corresponds with a similar state found in other serine lamelilbrencha* Its larval function in feeding has to be taken over by soms other organs, ultimately the gills* 3 9 . This will he discussed further in the section on gill development* The functioning of the byssus gland at spatting is apparently common to a ll laraelllbrenche, even though in some cases, the hyssus gland is lost in the adult* Especially in littoral species, the spat would he liable to be shifted unless it was firmly attached or in a sheltered spot* In the Teredlnidae (Sigerfoos, 1907)* the byseus gland is functional for only a short period after settlement* The immediate development of the diseoconoh is import ant in providing additional protection, for the larval shell is extremely fragile* Further consideration of the spatting process w ill be dealt with in another section, and now the changes that take place in the various organs of the newly settled spat w ill be discussed*

The Anatomy of the Spat* S h e ll, The development of the dlssoeonch follows rapidly the transition from pelagic life* The shape end proportions of the spat shell are somewhat different from those of the adult, but this will be dealt with in the section on growth* Development of the molluscan shell Is treated in detail by Bhrehbaum (1 8 8 5 ), Bbderman (1 9 0 2 ), B ernard (1 8 9 6 ), Weymouth (1923) * Boggild (1930), Trueman (1942) and many others* 40* Mantle* Xn the young spat the mantle ehengee little from the single layer of epithelium, with sparse, elongated nuclei# The mantle edge still consists of the muscular and secretory lobes only# The third or sensory lobe does not appear until after the animal has reached a length of 1*0 ran# when it is formed by a longitudinal splitting of the outer secrdory lobe, and the groove so formed becomes the perlostracal groove (Pl*13» fig* 27), (Yonge, 1948)* Previous to the formation of the groove the periostraeura originated from the tip of the secretory lobe or from a point on its external surface (Pl*13, fig* 26 pl*)« The lin es of c ilia found on the inner mantle edge of the larva ore retained (P1.16, fig*35c) in the spot for some time as a row in the region of the future inhalent siphon* By the time a length of 1*0 mra. is reached, however, these cilia are confined to a depression (Pl*19 fig* 46- e* gr») below the Inhalent opening* The further history of this area requires to be followed* Both Harms (1909) sad Hebers (1913) for the Gnionidee and Anodonta eel leas Is respectively, figure end describe the dilation of the inner mantle edge but do not discuss the possible | | funet ion. In the literature there Is little reference to the formation of the lobes of . the mantle edge* Stafford (1913), gives r short description of the mantle of the/ /tin young spat of Oatrea vlnrlnloa* It is Interesting that the figures in his plate 7* show only two lobes in the 1*0 am* spat, but three for the spot 1*5 an* la length* Jackson (1890), mentions the raantle but gives no details cm its development, in £• virgin ice* Hebers (1913) considers the order of appearance of the three mantle folds in Anodonta cellensls, to be first the external, then the middle, and finally the Inner*

Siphons* Xn the fully grown larva there already exists the tisane bridge sometimes called the siphons! septum, Connecting the two inner lobes of the mantle* Through metamorphosis, this bridge retains its identity and becomes a more definite structure (Pi* 14, fig*28, s*s*), flg.31), (P1.15, fls.3fc). Soon after metamorphosis, the primary exhalent siphon develops from the inner lobes of the mantle edge as a thin walled membranous sac, open at the free end (Pi* 15, fig*33 e* si*)* A similar structure has been personally observed in Mya arenarla leas than 0*5 an* in length, though it has not been observed in life in 2* pullaetre* In £• arenarla* it is a very active organ and is rapidly extruded and retracted, much like a proboscis* Xt would seem essential that some such structure should be developed early in the sedentary stage in order to keep the mantle ehsnber and g ills free of faeces* 42* At a length of about 0*4 n* the first indica­ tion of the inhalent siphon takes the form of tentacular development in the region of the slphonal septum* Oroovea fora in the inner (muscular) lobe of the mantle edge ventral to the septum, penetrating inward from the free edge of the lobs* The tissues between these grooves thicken and elongate into definitive tentacles (P1*14» fig* 29, si*t*). The tentacles nearest the septum are formed first and are consequently the largest, while new tentacles are formed by further grooving down the lobe* This process takes place on each mantle edge and stages are developed sim ilar to those shown in ?1*14, fig*30; PI. 15, fig*34* Soon after a length of 1*0 mm* has been reached, although considerable variations may occur, the upper and lower ends of these two groups of tentacles fuse to form the margin of the inhalent siphon* At first this consists of 8 or 9 (Short tentacles which form the inner row of the adult siphon (Yonge, 1948)* Approximately at the some tin s, the sensory lobe of the mantle edge is formed and, no doubt, as the siphon grows and elongates, it takes with it a covering of tissue from the sensory lobe, from which the outer rim of tentacles of the adult will be formed (Yonge, 1948)* In PI* 15» fig.34, ee.t*, the first indication of the formation of tills outer ring of tentacles around the exhalent siphon is shown* On the development of siphons little information may be found in the literature* Harms (1909) indicate*/ /Indicates that the respiratory siphon of the Unlanldas is formed from the contact of two cone-shaped prolifera­ tions on each side o f the posterior mantle edge* On this opening appear small papilla-like elevations which become the "fio&rlee* of the siphon* Xeiseenheimer (19(H)# leaves the siphons out of his extensive work on Drelaaenela as being of secondary importance* Hebers (1913) brlelfy describes the formation of the siphons in Anodonta cel lends* A bridge is formed by the fusion of the two sides of the inner lcbo of the mantle and under this appears the first sign of the anlage of the respiratory siphon (* Ateoslpho9) • Wasaerloos (1911) describes the formation of ths siphons in Cycles cornea and shows it to be a double fusion of the posterior part of the 1 Mont elf alt ef , the exhelant siphon being formed first and then the inhalent* There are no details as to whether a particular part of ths •jtantelfalte* is involved or whether it is an overall fusion which, from the figures, it appears to be* SIgerfooa (1911) shows the larval Xylotrva gouldi to have siphons and they are also found la tha larva of Zlrohaea crlaaat* (Werner,

In connection with the development of the siphons is the local enlargement of the palllal muscles to form the siphonal retractors* They originate from the muscular lobe of the mantle near ths siphonal septum* They begin/ kkm /begin as short muscle fibres which extend posteriorly into the mantle (Pl*1h, fig* 30, p*r*m«H As the an Inal grows they extend end radiate oat antll they cower an arc of nearly 180°* Pi* 13, fig*27, p*r*m* and PX*15, fig*32, P*X*m*, show cross and horizontal sections respectively through these retractor muscles*

H i l l s * The significant change that occurs in the gills of the newly settled spat of J[* m lloetra ie the develop­ ment of the adult type of dilation, which has bean described many times, Peck (1877)* Pelsoneer (1889, 1892), Ridewood (1903), Orton (1912, 1913), Tonga (1923, 1928), Atkins (1936, 1937 *~e, 1938 a~e, 19U3) end others* In addition, there is a continuous increase in the number of filaments, from the larval munfter of four, to approximately twelve in a spat 1*0 am* long* With the lose of the velum, the gills must be assumed to become the food collecting organs of the spat* However, as pointed out by Yong^(l9M7) , the filament a eannot function as food collectors until the food groove is present* In X* jsUgglgi* os in moat of the other species that have been studied, the food groove does not appear until after the "reflection* of these first formed filaments has occurred, not until the spat is nearly 1*0 mm* or more in length* It is therefore necessary to postulate a method of feeding other than that involving the food groove* Details of the exact method must await the examination of/ %5 . / e t living material* It is doubtful if the palpe am as yet functioning aa sorting mechanisms* They are funnel- shaped, oliieted on the inside and directed with the opening toward the ventral margin of the row of filaments* This ventral margin may act as a temporary food treat* The palpe are relatively large structures, and it would not he necessary for the food directing rrech&nlesi to he finely adjusted for the food particles to strike the palp area* Ho doubt the rapid development of the adult type of etenidial eillation is associated with the g ill becoming functional as a feeding organ* The method of increase in the number of filaments is most easily oboorved in the spat, although it is evidently a continuation of the same process in the larva* Attached to the siphonal septum are two bloeks of tissue, one on each side of the median line, which are the the gill adagen* From each of these are "budded" off (to use Lankaster* s term for the process in Plsldium (1875) sections which elongate into oliieted gill filaments* These form the outer lamella of the inner desdbraaeh* The process is ahem In lateral view in Pl*1h» fig*29, and in frontal view in Pl*l6, fig.35* Laease-imthier1 s (18198) lucid description of the process in Ifcsrtllup edulls can hardly be improved* Thus the lamella is added to from the posterior, the oldest and longest filaments being the most anterior* The first filament, which is never reflected, is attached/ /attached to the visceral mass, with the ventral «od lying between the upper and lower palps* The free ventral tips of the filaments *hloh are enlarged longitudinally are rather loosely united, prefoably by cilia alone* At a length of 1*0 ms* two well defined rows ox* inter- filamentary junctions are present and the free ventral edge of this lamella begins to fold inward and upward* This is the beginning of the refleeted (indirect or ascending) inner lamella of the inner deralbronoh* The further development of the g ills is beyond the seope of the present research, but parts of it have been Observed and they may be of interact* Soon after the reflection of the outer lamella of the inner demlbranch, the outer demlbranch begins to f a n along the axis by an upward growth of newly formed filaments* The process differs from that in MvtHus edulla (hs©aae«*Duthler, s 1856, Rice 1907) in which the corresponding growth la downward, but it is sim ilar to that described for Cycles cornea by Waeaerloos (1911)* In X* pnlleatga* the Ibisaat ion of the outer lamella of the outer demlbranch cannot take place by outward and upward reflection of the inner lamella* The terms 'reflected* or ’seconding* which ere appropriate for tha Umer demlbranch, are hardly applicable to the outer* The formation of the double lamella must take place as tihown by wesserloos (1911) for Cycles cornea by a bending or doubling downward of the single, first formed lamella* k 7 + This approaches more closely the method of g ill formation suggested by Tongs (l9k7) based on functional and theoretical considerations* However, there still remains the question of the formation of the food groove, of which there is no evidence before the bending or doubling has Ptkkaa place* In addition, there is the formation and disposition of the otenidial bloud veeoels to be considered* Ridewood (1903), Rioe (1907) and especially w&seorlooe (1911) have reviewed the literature on g ill development and since that time there has been little or no work on the development of that organ in Icusiell ibranchs* The mode of g ill formation in X* onllastrs throws little new light on the subject* The Inner denxibranehs of both BgtilHfi fifltillE and £. oullagtrs are formed in essential­ ly the same manner, but different from that of Cycles cornea- The outer damibranchs of £* «■»* £•,9 ,9 m m to be formed in a similar manner, but different from that of £* edalls* In addition, Rice (1907) found the farma- tion of the later filaments to be different from that of the earlier filaments* This brings to mind the often used quotation from Rice (1896) regarding the extreme plasticity of the lamellibraach gill* It is becoming increasingly evident that functional interpretation is required to go hand in hand with morphology in the study of development* ' Foot egg h w a Olaafl. The byaetue glcnd become fruactionrl the time A of metamorphosis when the gland becomes connected with the byeeal groove* The foot beccnee Shorter end broader, but the dilation is retained (?1*19, fig*fc6)* The byseus gland meres further buck Into the foot md becomes relatively smaller*

The nervous sytem changes slightly at meta­ morphosis with the alteration In the position of the cerebral ganglia and their fusion with the pleural ganglia* The eonnectivee now become evident* The atatoeysta and etatolithe increase in else* Immediately below the visceral ganglion, a pert of the epithelium becomes specialised Into the sense organ described ae the esphradlttffi (P1»16, fig* 3 8 , o*s») which is evident when the animal reaches a length of 1*0 mm*

O.teeot-lve System The major change in the digestive system ie the alteration in the position of the mouth and oesophagus* Chi the disappearance of the velum they move dorsally and to the anterior until the month lice iraaediately in front of, and on a level with, the anterior adductor muscle (PI* 11, figs* 18, 19, 21)* In the earliest spot stages it is close to the adductor, but later moves a short/ b9* /si#ort distance bade from It* Up to a length of 1*0 am*, the mouth opens directly downward, while the oesophagus, now relatively shorter than in the larva, bends round to enter the stomach (Pl*19, fig*U6 o*e.s*) The stomach enlarges rapidly and the posterior end is tilted downward, bringing the style sac into a more vertical position (Cf* P1.9, fig*1h and Pl*19, fig*h6)* The intestine extends back parallel to the base of the stomach, behind which it bends sharply upward (?1*19, fig*i|£, i.n*t.*)* It makes a short loop in the vertical plane to the right and proceeds almost to the dorsal lim it of the body where it bends to the left in a horizontal plane, with the loop partly overlying the stomach* It now passes directly backward along the dorsal body wall and as the rectum^ passes through the heart and pericardium (P1.19, fig*h£, r,p,h*)* It then circles behind the posterior adductor to which it is Closely applied, and bends far back on Itself to end in an anal bush just below the visceral ganglion* The digestive diverticula (P l*i6, fig*38 d*d#} undergo no in^ortant change other than increasing in slse with the formation of numerous branched duets* They cover the visceral mass in the anterior dorsal region and the ducts enter the anterior pert cf the stomach at the upper lim it of the style see* 5 0 . B f f r t ffml P ffrta rfli.m i The heart and pericardium, together with the kidney, are generally assumed to originate from a common anlage, which takes the form of hands of cells just anterior to, and shove, the visceral ganglion and posterior pedal retractor muscles (Ueiesenheinrr 1901, Habers 1913, Fernando 1931, Krdman 193h)* The anlage could not he identified with certainty in the larva of £♦ oullaatre- hut the appearance of the three organs in the spat was unmistakable* Xn a spat of 0,28 new the thin walled pericardium appeared as a comparatively long shallow cavity surrounding the rectum, extending from the posterior end of the hlng ligament to the posterior retractor muscles* The heart showed as a double menfcrane tightly enclosing the rectum hut as yet there is no cavity* At a length of 0*35 nnn (?l*17f flg*l&), the develepmeat from the preceding stage is considerable* The external heart maaferene has now separated from the internal to fora a cavity surrounding the rectum* The heart is surrounded by the pericardium which is bounded to the peaterlor by the kidney* A sagittal section through the heart, pericardium and kidney of an animal 1*0 mm* in length (Pl*17, fig*h3) , Shews the muscle fibres in the heart wall just beginning to appear* The larval kidney could not he identified with certainty* Very soon after spatting, in animals 0*28 an* long, the beginnings of the kidney were identified at the/ /tto posterior end of the pericardial cavity, against the posterior retractor muscles. The organ consists of a paired vesicle with occasional groups of cells which reaenble the excretory cells of the mature kidney* In an animal 0*5 *»a# in length it is a shallow body with a central lumen, lying anterior to, and vertical against, the posterior retractor muscle (P1.17, fig*U0, k*)* A diagrammatic reconstruction of a kidney in an animal 0*5 an* in length is shown in Pl*17, fig*39* The frontal view la shown with the upper part of the figure corresponding to the dorsal part of the organ* A. and B* are oross sections in the regions indicated by the two lines* In Fl*17, figs*M and U2, are shown reconstructions of the right half of a kidney in an animal 1*0 ran* long; and P i.17, flg*h3, k* Shows a sagittal section of the kidney in an animal of the same size* The gland consists of two tubes, one within the other* The inner, thinner tube is the rano-perieardial duet which leads from the post era- ventral part of the pericardium into the dorsal pert of the exoretory section of the kidney* The direction of the current is shown by the disposition of the cilia in the reno-*perio&rdial duet. The excretory pore discharges near the reno-peric&rdlal opening into which w ill later be the suprsbraaehial chanber* Ho ducts are evident in animals 0*5 msu In length* The two lobes, right sad le ft, of the kidney are united by a connnmicat lag tube below the rectum* 52* h a te * the walls of the kidney become greatly folded in order to Increase the surface area* H ebers (1913) considers that in Anodonta oellensis the kidney is so well developed that the rano- pericardial duct functions shortly before the beginning of the free living period* Comparisons are difficult but there la certainly no evidence of the kidney being able to function in £. oullastra until a length of at least 0.5 mm* has been reached* Ohdner (1912) in h is extensive work on the morphology and phylogeny of the lame 11 ibranch kidney describes that of Venus galllna as a representative of the Venerldae* The structure of the kidney of the adult £• nuUastre is similar to that of Yfttta galllna- but both are different from the organ found in the spat lees than four or five am* in length*

Honed» In aniraalo 1*0 mm* in length the gened appears as a small cluster of cells attached to the outer aide of th e w all of the ventral pericardium (Pl«19, fig*h6, £«)•

fto fat* of the Telmn. The most drastic anatomical change that occurs at metamorphosis i s the loss of the velum* From sections of a number of newly spatted specimens, In only two was found any evidence of what might have been remains of the velum* This consisted of cellular debris in the mantle c a v ity in the region of the mouth, which did not exhibit/ 53# /exhibit the normal dear-cut outline* It appears from this that the bulk of the velum is sloughed off and that the operation is a rapid sad effective one which occurs aeon after the larva ceases to be pelagic* With the loss of the velum the mouth and oeso­ phagus are free to dorsally and to the anterior, taking with them the cerebral ganglion and the apical plate* As shown in Pl*9, fig* 14, these organs were closely associated in the larva* The pleural ganglia have now become fused, or nearly so, with the cerebral ganglia which take up a position adjacent to the anterior adductor anode (Pl*11, fig*21, c*p*g*). The apical plate maintains approximately the same relative position that it did in the larva, and as comes to lie directly above the mautlu Zt is presumed by various authorities to form the beginning of the upper palps* This also appears to be the ease in X* PBllastre. for in the earliest spat the tissue of the palp region is identical to that of the apical plate (Pl*11, fig.18, a*p*)« In Pl*12, flg*22 is diown the mouth region in frontal section in a newly settled spat* From this origin the upper palp grows rapidly and at a shell length o f 1*0 m u they are 0*1 msu long. The 1*2 m u sp at o f ftstvjfa edalls described by Tonga (1926) also had relatively huge palps* Up to a length of at least 1*0 ms* the upper palp forms a hood above end around the mouth (P1.12, fig* 25 u*p* , fig*24 u*p*)* In PI*12, fig .25 is shown a seml-dlegrammat 1c/ 54* /semi-dingr eam tlo drawing of the palps dissected from an animal 0*75 &au long* After severing the oesophagus the whole was dissected eat as a unit, which as# Indicate the close tissue relationship between the upper and lower palps* The origin of the lower palpeio, however, debatable and there ie the suggestion that they originate as out­ growths of the upper* The definite break in epithelial structure between the lower lip of the mouth and the lower p alp is shown in Pl*11, flg*20 j.Ri*p* The mouth and oesophagus are lined with ta ll columnar cells with lightly staining nuclei and the palp with more cuboidel cells with heavily staining nuclei* It would therefore appear more likely that the lower palps are outgrowths of the upper* Loven, as early as 1848, associated the develop­ ment of the palps with the apical area of the velum, and Hexfee (1875) suggested the velum was transformed Into the palps* Devalue (1852) believed in the shedding of the velum toward the end cf larval life* Ryder (1884) working on the metamorphosis of Octree virginfoa. agreed with none of this* Sigerfooe (1908) believed that the velum of the Tenedinidae is suddenly cast off and eaten soon after the attachment of the larva end that, as a consequence of this lose, the formation of the palps has no connect ion with the velvmi* S ta ffo rd (1913) d iscu sses a t some len g th th e theories of palp formation and questions whether the velum has anything to do with the palps in Octree virglniea- 5 5 * Jan !m m (1890) speaks about the palps end the velum existing at the same time in &« vlrginlea. Field (1922) studied the formation of palps in Mart Has edulia from whole mounts only, and came to the conclusion that the develop­ ment in 1« edulla is ©indlar to that worked out for Drelseensla polyraorpha by tteleeenhelmer (19(H)* While much research has been done on the SevelogH&Dnt of freshwater lamellibranchs, most of the species studied have no veliger larvae and the palps are described as originating either from papillae as in (Habers 1913, Harro© 1909), or as outgrowths from the upper and lower lips of the mouth as In Cycles (Ziegler 1865, W&ooerloos 1911)* Medaaenheizaer (1901 in h is very detailed paper on DrelsaenBla describes the upper palps as originating from the apical area* He also described the formation of the inner or lower palps as "outgrowths of the posterior end inner side of the outer palps*" Col© (1936) again took the question of palp develop­ ment i n Outre** a d u lts and he agrees w ith K eissenhelm ar a s t e th e mode cf form atio n . 3S. The Spotting of Yeaaruple nullestra on Plana Bia*.— . I t la known th a t o y s te r la rv a e te n d to s e t more readily on tinder surfaces of various cult oh material a* 8ehaeffer (1937) has demonstrated a functional relationship between the angle of surface and the frequency of attach­ ment of the larvae of Ostrea glass in Quilcene Bay* Essentially the same relationship was found by Hopkins (1935) f o r SI* lofrlfla. They attempt to ascribe this setting behaviour to a "negative geotroplsm cap to the purely mechanic el factor of the swlmaing position of the larva where the foot and velum are uppermost, and vould therefore most often, fortuitously, come into eontoot with under surfaces*n (Schaeffer 1937)* The swimming position of the larvae of £« um ioatra and most lone 1 lib ranch veligere is not different from that of the oyster* It is not Imposs­ ible for byesus attaching forms to settle on under surfaces, and in & few instances, this has been found to occur* Experience has shown moot non-cementing species prefer to settle on the upper surface of cultch material* On beaches, the spat of £• nulla a t re a re moot o ften found attach ed t o the under edge of overhanging lodges an pebbles and snail stones* To gain some information on the setting behaVour cxf £* m dl^stra the following experiment was carried out* Him 4" x 4" ground glass plates were held at various angles in frames of mesh galvanized wire* These were duplicated with plates of Tufnol (trade name for plastic sheeting). Four sets of nine plates were hung 18" / 57* /18° below the surface, from a raft moored off the s t a t io n d ip , previous experience having shown this to he an excellent settling are a# The frames were hung free t o swing at random relative to the direction of the current, which in the region of the raft does not conform t o a dtscemable pattern* It is probable that the frames would swing so as to o f fe r rotnimuta re s is ta n c e t o th e p r e v a ilin g current, i*e« parallel to its direct.ion* In this case similar amounts of water would flow ever a ll surfaces regardless of the angle at which the plates wore held* Partial dogging of the meshes of the wire frames with algae may have altered this* The frames were placed d o s e together to insure equality of exposure end remained in th e sea from July 25th to Septeaiber 2nd, 1947, during which time no storms occurred* The detritus from the upper sides of the plates was examined in a counting cell. In addition, both sides of tbs plates woro examined under a binoocular microscope* Both spat and settled larvae were counted, the la tte r being assuued to be undergoing metamorphosis*

R esu lts. Ho spat were found on the under surfaces of p iste s* This corroborates many other observations on fist horizontal collectors, and this behaviour appears to be typical of most v e lig e r s which do not become permanently attach ed like those of the oyster* Even in the Anoraiidae a slightly higher proportion of larvae settle on the upper su rfa ce of cu lt eh m aterial. %. .. The count e given In Table 6# Indicate a good correlation between the frequency of spatting and th e angle cf the settling surface; the greatest settlement occurs on toe upper surfaces «Mch are nearest to the horizontal* As clea rly to Table 6 , and to the graph 3*1*21, thews i s l i t t l e difference to the esaunt of eettlemcint on g la s s and ou T ufnol; and toe ap plication of a t e s t of eignifi- can es proved no d ifferen ce s ta tis tic a lly * The o r ig in a l intention in using g la s s was to fieteriato© whether lig h t exercised eiy influence ok the setting behaviour* However, the upper aurfaeea of the plates, even those tooltoed at a etaep angle, were soon fouled by a coat tog of detritus ohich prevented the transmission of light* B am spatting took plao© on the Inclined plates* The areas cf these were pi*o jested on to the horizontal, and the aac&er of spat per square Inch calculated* The following results were Obtained and plotted on tbs graph P I. 20.

Ah u in T o ta l fsoiwittA • 16 16 5*0 5*0 3® 16 12 4*6 6*2 *5 16 « 4*8 7*0 60 1 6 h 3*0 12*0 9® 16 0 0*0 0*0 1f l t t f §*

IfifiSLS BQ l HZ sa sL sa s MMSP X T T i I r i iUBOlft T uftiol > round «1»m

ffiate— of B P B t Huntier o f .p a t 270 96 09 300 95 6a 919 m 71 990 m 00 360 ■ 0 0 90 06 10 OS W so <0 99 n

'90 ■ -«9 n too 00 112 t95 09 61 tso 00 99

■ 0 O' m 6a 90 225 so 19 245 9 0 6a » ♦ When t]&* total exposed area is considered, tbs efficiency of the plates as spat collectors decreases as the angle of the plate Increases; but when the areas are projected on to the horizontal, the efficiency increases blth the angle* Theoretically the curve for the projected areas would continue to rise after the 60 degree point, but since no spat were caught on the vertical plates, a zero value le graphed for the efficiency of the plate held at that angle* If the setting was the result solely of gravity, there would have been an equal catch per unit of area on projected surfaces* But this was not found to be so, for / the plates held at an angle proved to be moat efficient. Therefore, it appears that the setting eot is due to a horizontal movement of the larvae, and this is doubtless brought about by currents striking the faces of the plates* On the other hand, upper and under sides of all plates, regardless of angle, were theoretically exposed to equal amounts of flow* The non-settling on the under and vertical surfaces may be explained by the lock of fouling* If equal amounts of water did pass all plates, then all of them, If equally fouled, should have caught equal nunfcers cf spat, regardless of angle, total exposed, area, or of projected area* It nay be concluded that the supposition that a ll plates were equally available for settler® nt does not hold good, possibly because, owing to the fouling of tbs meshes, the frames did not swing as anticipated* The/ 60« /T h e conclusion that the setting act is due to a horlsontal ca r r ia g e o f the mature larvae in currents which strike the plates taore o r less at right angles, coupled with Initial fo u lin g o f the setting surface, seems to he valid under the conditions of this experiment* K elson (1926* 1927)* P rytherch (193W # C ole and K night Jnes (1939) » K orrin g s (19UO) and others, have investigated the relationship between the number of oyster spat and the angle of the settling surface. Korringa (19^0) is the only investigator to find that more oyster larvae C&+ ftdftlis) settle on upper than on under surfaces* No adequate explanation has been given* Korringa (I9b0) gives the guarded explanation that it is the result of the efforts of the mature larvae to attain their ecological norm. 61.

The large spatfall of £• nullaatre In Belloch Bey from the breeding In sunnier of 19^6 suggested the possibility of following this brood so go to obtain infor­ mation on its distribution relative to tidal levels, its mortality and its rate of growth. The beach as a whole does not conform to a habitat for ][. oullaetra. so this spatfall also presented the opportunity of determining whether the small population of adults was das to unfavour­ able habitat or to normal lack of spatfall. After larvae had disappeared from the plankton, three one-square foot eagles of beech surface, to a depth of two Inches, were taken from each of 7 stations in a line running from high water mark to low water mark, on a spit in the centre of the Bay* The stations were placed at thirty yard intervale down the beach, and their tide levels determined by taking the times at which the tide reached them on a calm day, and finding the corresponding heights from methods given in the Admiralty Tide Tables for 191*7 » Supplementary Tables, page 22*9* The stations were found to be at the following tide levels: 3.0, 7*0, 5*0, h*5$ k*0, 3*0 and 1*0 feet. The beach along the line of stations is coov>csed mainly of a fin e la y e r o f sand to a depth o f 3 t o 12lnch0S, overlying, a bed of clay. The whole area is scattered with fa ir ly large boulders (P1.22, figs. 1 and 2). Various dispersed areas are studded with small pebbles 1.0 / <2# /1*0 to 10*0 cm. In diameter, and It is in these regions that the maxima® spatting of X* PQllftstra occurs. Flattsly and Walton (1922) Appendix 111, give a descrip­ tion of Balloch Bay. The tidal streams in this area have not been studied in detail, hut there appears to he a current parallel to the shore, especially on the ebb, with a strong likelihood of an eddy on the flood tide, caused by the projection of Clashfarland Point (Pl.3, hap), which merles the southern extremity of the bay. The beach supports a small population of Mara arcnarts and of X* especially at the lower levels, with Cardlum edule and ootpaM tlrely snail aorabers of YgflffrWPtB m illartM .

Sam pling. Stapling was done with a one foot square iron frame which could be pressed down into the beach* and the scad and grave1 taken from within with a small shovel. The candles were placed in cloth sacks as they were collected and taken to the laboratory where the spot were separated out* Hits was done first by sieving the whole eample through a 1.73 mm. cash sieve. The residue wee carefully picked over and all the pebbles and rooks examined, soon under the binocculcr microscope. in this way the larger spat were removed. The finer sand which passed through the first coarse sieve, was than put throqgh another 0.73 an* aertu The residue was examined in a counting cell under the binocular microscope. A nu ber of animals lese/ * 3# /less than 0*75 m* vers obtained* indicating the possib­ ility that pert of these smaller else groups was lost* A more refined method weald here been prohibitive in tine* All shells or parts of shells, as well es the living animals, were taken and counts made of the animals living at the time of sailing, of the complete single valves, and the number of single shells drilled by gas­ tropod, which was taken as the ntiriber of animals bored* To arrive at an estimation of the number of dead animals, the number of uribored single valves was multiplied by the factor 2/5* This is a more suitable conversion factor than 1/2 because the chances are greater that more single than both valves representing a pair, will be found* In estimating the ous&er of valves from fragments, any part that could net be duplicated, such as the hlx&e, was con­ sidered to be a single valve* The complete data is tabulated in Table 7# The firs t sampling was done in September, 19M», and farther samples were taken in Decenfeer, 19M>, February, April, June and October of 19U7* The sample from the 1*0 foot level in the October samples was not obtained until a month later because of the unsuitable tides*

R e su lts* I n FI#224- is shown the distribution of the spat over the beach for the 19M& and the 19h7 spatfalls* A striking feature of the graph is the sim ilarity in density/ TABLE 7 . J&SLS2 the dead M b s ill £ SSI eanro ear sea, AMfll. Juno m3 * Wovenfcep. tSk?. * Sample not tekan.

S ta tio n 2

iB 2 S 2 l

2 Q S 2 1

imwummmviK* wm*m* 1 H 1 n * * - h i m 1 W « r MKVKKf i r . i K *ilIJr JM*I»^*Maift?Wi NK I3»j M l*

S 5 a a &< Sftff fffPti te^JiK^e toJLtob jgoMfffflsa) . the nanfrei twed end tl 8OTB»«g f pot from

I t. £ m S L J2*. AXI to and Dead jm iW L—am.Pgq Veto ApI Jan Oct Sep Poo FeV ApI Jan Pot rABDil 8 . ata.Ugtiea. of the iw ta U ly parolee ^ roat fromTOrlcme as&\i/mMaeBoureaentg i&aagi*w , thoea of length and areiate»aQ glvxm la aa.

S ta tio n Sam ple Benge ■eon 7 e rla n e e S ta n d a rd Standard i e ls e O « v ln t10* B rro r

m .

...... i ..... _ 3 • i .. k1 0.75-Jfc.at StU7 0 .8 0 2 0*131 . _ .t ...1... 3*75 . 3 .. 65 0*75 ~ 5*56 1.002 t*QUk „ 0 .0 1 6 ...& * t 125 0.75 - 5.16 0 .6 0 9 0*925 ... 0 .0 8 3 ....! i- .... . ,-,-SL. M l. __. 0.75 - 7.9k -•U M l. 0*099 ^ .. -„irrr..ft.. 166 0.75 - 5.56 tfllk - 6 .9 2 0 .. .0 .9 5 7 0*123 ft - A * .2*66 0.706 0.853- _____ 2 255 0.03 - 5.18 1* 52 Q.7U8 0 .908 0*05S - ...... S -M. 0.37 - 5.18 0 .3 9 7 0.656 0 .6 * f nyj ft - 1 _ 1 7 . 0.75 - 2.18 1*37 0.110 0.3ti0 O.Oft^J 2 US 0.75 - 2.56 1tS1 0 .2 0 9 . 0 .k 6 5 f t - 20-... 0.75 - 3.68 1.6k 0.k37 0.685 7 - 1 iSiiQ 0.57 - 5.56 1 .5 k 0.U59 0*709 0*027 2 518 0-37 - 5.16 ....i» m.... - M 3 L - /G en eity end distribution between the two years* This would appear to indleate that the phyeloal nature of the beaeh is the essential factor* for this la relatively constant* Similarity In density did not occur In the case of ffira arcnaria and Cardluia edulc. for the former species spatted light1y In 191*6 and heevily In 19U7* while the latter spatted heavily la 19M> and lightly In 192*7* Xt is believed the low value for £• nullastrs et the tide level of 3 feet is due to the unsuitability of the ground for setting* as It is couponed of nearly pure sand* and thus provides no attachment for the byssus* Stations at the 5*0* 7*0 end 8*0 foot tidal levels ere much cf th e same nature* although* doubtless* th e h igh level on the beech may account in large measure for the email spetfell there* Returning to the low value at the 3*0 foot level* it seems unlikely that in the short distance between this sod the h»0 and the 1*0 foot stations* there should be any factor such as tidal swirl to prevent initial spatting* when this was heavy above and below* The absence of natural eultch either prevents setting; or* if there is setting* survival beyond the earliest stages after mats- asrphoete* A sample to k e n below the aero tide mark at the outer edge of the seme failed to jttLd any spat* and here again the bottom Is of pure sand* to c ts liS x * The reduction in the number at spat per square foot throughout the y e a r i s shorn in Table T» and th e m o rta lity r a te on P la te 2?* By June 19U7, the mortality had reached nearly 10C$* The nausea may be tentatively attributed to throe fact ores 1* The unusually se v e r w in ter o f 1$tt|6-4|.7* 2* Predators* 5* General unsuitability of the habitat* It le true the winter of i9U6-4#7 *ae unusually severe* but no drastic effects were noticed on other invertebrates in Balloeh Bay* Sampling at Cross Houses Beach disclosed no heavy mortality of X* udllastra there* though the original numbers were not large* it is doubtful if the severe winter played a significant part in causing the excessive mortality in this brood of X* shllaatra* Probably three types of predators have to be considered* Balloeh Bay is the feeding ground for large flocks of several speeles of shore and sea birds9 such as gulls, curlews* oyster catchers* red legs* elder end mallard ducks* It is known that these types of birds do fe e d on small mellusks* and even a small number of birds feeding regularly over a period of nearly a year* could snake a considerable inroad in a population of litto ral aollusfes* especially in eueh a favoured feeding ground* Fish are well known to feed on small mollusks (Davis 1923* Blegvad 1928, Peterson 1915)* F la tf is h are known t o / «6* /to frequent the intertidal soaee of Balloeh Bay during high t ide so evinced by their tree** in the sand* A third typo of predator is the d rill or gastropod borer* Approximately gC of the deed epat had been drilled* This Is e minimum figure fear it is likely that s drilled shell w ill break up more readily then an undrilled one* Bunt (1925) considers that Katies Is responsible for the numerous drilled shells of bivalves in the Plymouth ares* Zt is believed that the main cause of mortality in Balloeh Bay is the unsuitability of the ground for older spat* The surf nee layers of the beach In which the young spat moat at first maintain themselves la not a stable environment and the surface layers of ©and shift about considerably* This was observed: one instance was the appearanee* 0 ver the winter* of a bed of fossil Lntrarla and Pact an shells to one side of the station at the l|*0 foot level* Thus the young spat, along with the holdfast* any be buried by shifting sand* At this stage the siphons are not more than k ~ 5 am* long in the larger specimens* so it does not require a deep layer of sand to smother them* On the other hand, they my bo more exposed by the shifting of the sand to predators or to wave action* The thoovy of the instability of the environment is further supported by the feet that the small adult population on the beach la found between the 0* and the 2*0 foot tide levels; an area where boulders and pebbles provide good protection for both the young and old* 67* The Cross Houses B ach et M illport, which supports the densest population of V* pullagtra on the Island is nearly a solid mas- of large flat rocks providing plenty of attachment and protection; an extremely stable environment as far as movement of the substratum is concerned* From the small adult population on Ballooh Bay it seems that a high mortality is not unusual* Two similar species are found in British Columbia, the indigenous Papilla stamlnea and the imported Japanese Paphla nhUlP ioarup; but their habitat Is different from that of Venerunic t>ulU stra* They prefer e protected beach of mixed gravel, shell and mud* It is not known whether X* nulla at re is found in such an environ­ ment, for the writer ha© seen nothing comparable in Scotland* All beeches on the Isle of Cumbrae are exposed to wave action that at times may become considerable*

It is striking that the rate of mortality of a large population such as that of young V* pulls stra in B alloeh Bay should be bo high as practically to destroy the whole population within a year* Such occurrences are not unknown in other species, for bey mouth, McMillin and Holmes (1925) record a mortality of approximately 66?. for the spat of Bilious uatula on Copal is Beach, Washington, between August, when they settled, and the/ 6 8 . /the beginning of December* A storm in th a t month reduced the numbers still further from U9 k per square fo o t (th e 33 f survival level), to 18 per square foot, and by F bruary these had been reduced to 16 per square ) fo o t* Few, if any, were reported in the following sum er. Thus it. is seen that a heavy set o f clams, originally 1U5 0 oer square foot, may bo completely destroyed, even when they have settled in the type o f habitat which is optimal for the species. Therefore, In comparison, one might expect considerable mortality In Balloeh Bay, for It does not represent a habitat in which the adult X* r>ul I a stra is found in greatest abundance. This raises once again the problem o f meta­ morphosis, choice of substratum, delay and mortality. Thopson (19M>, PP« ty60-U67) has discussed this at some length and concludes that the "either, or ” hypothesis o f settlement of ®rine invertebrate larvae is not tenable# Belding (1912) was among the first to point out that the survival of la mellib ranch larvae depends on the character of the bottom in which they settle. Kelson (1928) puts the matter succinctly when ho said, ”!Vhen the time for settling arrives, the larvae must attach or die*” Yong© (1937) assumed that the survival of the two species o f Arsorrhaia in Herdla f 3lord depends on whether or not they settle in the habitat for which the adult is adapted,/ 69 * /adapted, but that in an intermediate region both species are able to exist# Thorson (1946) cites Mortensen*s (1921) experiment in which he was able to induce metamorphosis in the larva of the echinold Melllta sexlee-nerforata by adding sand to the dish in which they were living* Day and Wilson (1934) • and Wilson (1937), have shown that the larvae of various polychaetes are able to postpone metamorphosis until a substratum suitable for adult life is encountered* It is significant that Thoreont s most convincing date comes from laboratory experiments* Larvae of Branohloma veslcuXosura kept by Wilson (1936) had a fairly suitable substratum available, but there was considerable variation in the time of settling. Lamellibranch larva© are very difficult to rear in the laboratory and the results, in relation to time, of such experiments must be treated with caution* Russell (1934) say©, "It is possible that the settling down of pelagic larva© is a much more precise and complex affair than we imagine, involving specific behaviour acts or trains of behaviour *11 It is not unlikely that the larva© of marine invertebrates have a certain power of selection of their environment for settling in; witness the search of the larval oyster for a clean surface; but the larva 1 s horizon is limited because of its size* A larva of X* pullestra may settle in the thin film of detritus and sand particles on a glass plate and this is suitable/ 70* /suitable enough for the spat, because the thickness of the film is adequate relative to the size of the spat* But it very soon outgrows this environment. What must be considered is the comparative size of the coeraoe of the larva or email spat and the cosmos of the adult* Suitable setting grounds for the larvae and spat of X* nulla stra are common, but there arc few habitats suitable for adults* Balloeh Bey provides environments suitable for the spat, yet few adults ere found there, and all the mortality cannot be attributed to predators. Many more examples might be given but one w ill suffice. Both type8 of ground inhabited by Aporrhala (Yonge 1937) we no doubt suitable for the newly settled larra of both pes-nelicanl and serresleno. The m ortality may m i l take place after the young have out­ grown the la rv a l environment and need the more r e str ic te d environment for which the adult is adopted. No amount of delay in metamorphosis or occasional "touching down” to test the substratum as they are carried along by the current, as suggested by Thor eon (1946, page 465)* can overcone the difference in the needs of the ; metamorphosed larva and of the adult. Careful examination of a variety of surfaces in the littoral and sub-littoral zones reveals the spat of many different species, often in considerable numbers, in areas totally unlike the adult habitat. Not always is the settling area even suitable for the young spat. 7 1 . This period after setting, possibly up to a year after this, is the stage in the life history of many sessile marine invertebrates at which considerable mortality occurs and this is certainly the case with X* nulla stra. Contrary to the new school of thought on the subject, it is still believed that survival of the spat and final succees of any spatfall ia largely a matter of chance* It is agreed that the larvae, or at any rate the larvae of certain species or groups, may exercise a certain amount of choice in the selection of a suitable substratum, but it is a choice that in the main fulfils only the itaaediat.e needs of the spat. It also appears that in most cases the high mortalities suffered by many species after metamorphosis (formerly attributed to the period after metamorphosis) may be spread over a considerable period* This would oertainly explain the mortality of the 1946 brood of X* pullaatra m Balloeh Bay. 72. Bat* of T?ator Prosmalan. Considerable interest Is being shewn in the rate of water propulsion, or filtration rate, In various marine invertebrates, initially because of the economic and hygienic importance in oysters, but more recently in other filte r feeding organisms in connection with food intake and metabolism* Similar studies on £• oullastrs were undertaken partly for the latter reasons, but mainly to ascertain whether, and if so how, the filtration currents end consequent pressures are involved in the •pawning act* Direct, methods of study have been used where the siphons of the vxiSm l s concerned have been tapped by tubes or robber aprons and the actual quantity of water passed through these tubes has bean measured* Indirect methods have alec been used by aeasuring the rate at which animals were able to clear suspensions of various types o f particles# A direct method was used by Porker (1914) who measured the strength end volume of water currents produced in sponges by attaching e tube to the osculum# Placing the tube in a vertical position and observing the increase in height of the water In the tube in relation to that in the tank in which the sponges were living, he obtained a measure cf the pressure produced by the erhalent current# By measurement of the velocity of/ /of the floating part idea in the tube, he estimated the volume of water pumped and concluded that the current produced by sponges consists of relatively large volumes of water flowing at low pressure# For the sponge flnlnosalla he obtained a water flow of 3*2 litres per hour at a pressure of 2*9 arm of sea water. The volume estimations are criticised on the grounds of failure to realise that the speed of flow through a tube varies along its radius, the maximum velocity being at the centre. Allen (1914) using a similar method for fresh water mussels made the same error. He had difficulty in Introducing the tube because of the sensitivity of the siphons and obtained only a single reading which gave a rate of 1*4 litres per hour. Hecht (1916) measured the current pressure and volume of water pumped in the ascidian, Asciqifi atra and pointed out the differences in the current velocities of the atrial and oral siphons, together with the angle at which they work, as being factors in preventing the mixing of two streams of water. He also measured the velocity of particles in a tube Inserted in the oral siphon. The pressure was found to vary between 1.7 and 2.1 mm. of sea water and the filtered volume to be 7.2 litres per hour for animals of 100 grams weight. The temperature was not given. Hecht considers the energy distribution in developing the water current in A. atra to be quite efficient the pressure being just sufficient to overcome the inertia of the water. He also concluded that the volume of water/ 74* /water moved per unit of body weight varies inversely with the size of the animal, a conclusion which is in general supported by the work of Jorgensen (1943) on l&melllbraachs* Koleon (1921) modified the method of Moore (1906) using a robber apron over the exha lent area and obtained for fistrsa girjKlalca a value of 5*7 litres of water filtered per hour* hater he obtained a value of 26 litree per hour from a 4 inch oyster at 30° C* Gaiteoff (1926, 1928b) in a broad study on the oyster gill in relation to sanitation and culture, describes two direct methods of meanuring the flow through the g ill of Octree vlrrlnlos* I*i both methods a tube i® introduced into the closes! ehimfber and made fast and water tight with cotton packing* In the "tank" method, the oyeter pumps water from a tank in which It rest© into a measuring vessel which is connectod to the oyster by the tub© inserted in the closes! chanS)er* The level of the two vessels is kept constant and equal by overflow siphons* This enm ity is most neeecsary, for a differential level in on© direction, would cause a siphoning effect through the gills, while in the ether direction the g ill would be pumping against a pressure caused by the head of water* la the "©erratne-cone” method the tt&e inserted in the cloaca is connected to a further system of tubing allows measurasent of the velocity of s cone of carmine/ 75* /canine carried by the exhalent stream; then using a modification of Poiseuille9 s formula far stress line floe, the rate say he calculated* Galtsoff Obtained slightly higher values with the latter method and considers them more valid as a measure of rate of flow. He secured values of 2.5 to 2.9 litres per hour at 26.9° C. Nelson (1935) criticised the use of a tube in the eloacal chant)er on the grounds of interference with the operation of the branchial hearts and visceral ganglion, as sell as Galtsoff9 s neglect of the water flow through the "promyal" chant) er. Hodgson (1928) attempted to measure the volume of water circulating through the mantle cavity of Mvtilus jStjtg&h & 9 Initially and unsuccessfully by means of tubes and rubber aprons. Re then turned to the indirect nethod of determining the rate of clearing of suspended material in known volumes of water. Using chiefly fine clay suspensions the rate was taken to be the time required for a xmnfber of animals to dear a known volume. While he recognised that the water, In which the mussels are placed, may be filtered several times in order to clear it completely, no quanti­ tative adjustment was made. The rate was found to be 2 litres per hour at 17° C. Hopkins (1933) studying the relative rate of flow of water over the gills of Patron gigaa used a method in which the normal functions of the animal are not interfered with. Re found the relation temperature and opt Imam g ill activity similar to that obtained by Galtsoff for 0* vlrglnioa. lying between 25 and/ 76* /and 30° 0* at which point the maximum rate of flow la 3*9 lltree par hour* Hopkins, however, believes the optimora temperature for feeding, considering tlia animal ae a whole, to ha about 20° C., for above this temperature the reives begin to close and eo aot as brakes to the water current* Sparck (1933) in a preliminary investigation on the power of filtration in £• edulls resolved the problem into how large a bulk of water is at the disposal of the anim al i f the surrounding water is almost completely calm* To solve this problem he plaoed an oyster in a veseel containing water of a salinity of 30# • Above this was a layer of water coloured with methyllc blue with a salinity of 21#,, and on top of this a layer of freah water to prevent evaporation, cooling, and the formation of vertical currents In the salt water, other than those produced by the oyster* At a distance of 30 cm* an adult oyster was able to produce a disturbance in the coloured layer by clapping the valves, but no mixing was effected* Fuller and Clarke (1936) in a study of setous feeding of Galanas investigated the rate of filtration by the speed of removal of carmine particles from a suspension in Which the animals were living* They calculated a figure o f 5*61 cc* per day, but made it clear that theee experi­ ments were preliminary, end calculations baaed on nutritional require;:ients by Marshall, Nlcholls and Orr (1935) Indicated that the values obtained were far below the volume sufficient/ m /sufficient to supply the nutritional seeds of the animal# hater Fuller (193?) again attempted to estimate the feeding j* te Of SffZMM U m EM m ' H" «** tw o fcjr a*torainlng the rate at which a group of animnle depicted cultures of th e diatom , HJtligffeMg# The form ula developed by him w as:-

Wx «• V 1n where Wx is? the amount of water swept free of diatoms by each copepod in x hours; V is the volume of water per cop©pod; 01 and 02 are concentrations of the diatoms at the beginning and end of time x« This formula is identical to the one here derived in rm othor way# By this method he found the sraeunt of water filtered per day was 1*09 cc# which, in relation to the amount o f av a ila b le food, would provide only ®m tenth of tha necessary nutriment estimated on the basis of oxygen aoneurtpt totu In & compreluxrt^ive paper, Fox, Sverdrup and Cunningham (1937) Hive a survey of the litsroturs and estimate the rate of water propulsion in the large California hm m I, ttrtilao oallfomlamua. Group* of nnaaaXa were placed in stirred suspensions of marine clay or calcium carbonate# The rate at which them lm l& removed the suapemsiou by filtratio n wsa ^eairored by chemical estlen- tien of the calcium content of successive samples taken at equal intervals of time* They made the assumption, "in u n it tim e each mussel pomps U litres of water through its qretem and removes a ll suspended calcium from this quantity of water,” and cm this basis they develop sn equation for tbs filtration rate* This equation is essentially the same/ 76* /e e m as those derived by Fuller and by the present author* Fox et &1 (1957) concluded that the mussel removes virtually a ll suepended^aatter from the water passed over the mucous surface of the gills and mantle, and that the water is propelled rhythmically and at a rate which is on the aver­ age constant* Medium sized mussels, between 95 and 130 am* in length, gave propulsion rates between the values of 2*2 and 2*9 litres per hour, with an average of 2*6 litres per hour# Jorgensen (19U3) studied the rate o f w ater transport through the g ills of young Msrtllup edulia by means of photometric determinations of the percentage amounts of the unicellular alga Svnechocoocus from a known quantity of the suspension of the algae* He obtained filtratio n rates of between 2*5 and 186 ml* of water per hour for a group of 5 animals, each 0*2 grains in weight, at o temperatures between 11 and 22 c# From the literature Jorgensen also calculated filtration rates per hour per gram for stages from the pelagic larvae (oysters) to the a d u lt (various species). These varied from 6*7 l i t r e s for larvae to 0*19 litres for young bottom stages, and 0*01 - 0*02* l i t r e s f o r ad u lts* In a study of the feeding of £• Virginias. booeaMff and Home^ko (19W) used the “tank* method of O altsoff (1928) modified by the rubber apron of Moore (1908) and Mela on (1921) over the exhalcnt aperture* Pumping rates for if. Inch oysters within the tenq>eratuw/ 79* /temperature range of 17*0 to 28*0° 0* averaged 2$ to 27 litres of water per hour with a maximum of 3k litr e s * to The rates found on the ebb tide were equal)/ or g re a te r th e n those found on the flood, thus refuting the generalisation by Kelson (1923) that relatively little food Is taken on the ebb* They conclude also that there ie no correlation between periods of shell closure and darkness and that the pumping rate is the sane for both daylight and darkness* It la pointed out that £» virgipiea is able to pump In one hour a volume of water 1500 times the volume of its own body*

The direct method of determining the rate of flow Is exceedingly difficult in the case of siphonate lem elli- branch* due to the great sensitivity of the siphons in most species* When tubes are Inserted In the siphons, and this can only be done during anaesthesia, they are later either forced out of the siphons or are cut by the pressure a t th e shells against the tube* The use of blocks to prop open the valves was unsuccessfully tried* In a few eases the Inserted tubes were retained In the siphons, but the animals did not exhibit normal reactions, and soon died* The alternative was the indirect suspension clearing method of Via Hanes (1892), Dodgson (1928), M aas (1935) and Pox, Sverdrup and Cunningham (1937)* The latter authors are th e only ones aho have developed and used th e method w ith any degree of accuracy, and it la / 88* /is their method, further modified, that wee used* The fundamental basis of this method rests on the assumption that the gills completely filte r out all particles in the suspension* Kellog (1915) considered that a lamellibranch was able to feed^nly when the water was comparatively clear, so that food particles would be brought to the surfaces of the gills a few at a time* Re maintained that in muddy water all suspended particles, whatever their nature, are led to the outgoing tracts* Re also describes the mucous production of ciliated surfaces and the large amounts of raucous that may be produced by continued stimulation* Damae (1935) describes the forma­ tion of mud deposits in the Zeebrugge roadstead by warms and mollusks, and indicates that colloidal particles ae well as detritus are filtered out of the water and deposited* Kansas (1926) describes the filering and depositing action of laraellibranchs, especially oysters and mussels, and describes the quantitative work of Viallanes who measured filtration rates by weighing dry the amounts of faeces and pseudofaeces deposited in a given time* Z obeli and Landon (1937) found that 99*9 % o f added bacteria are retained by th. gills of Mytilue calif ornianus. though Galtsoff (1928) states that only 20 - 30/ of the bacteria added are retained by Octree virgin lea. Jorgensen (191*3) assumed that a large majority of Synechoooccus cells which are only 2 - 3 microns long, ore retained by young Ma&HHSj SSUUa* !• vaHlaetn was found to be eble to clear suspensions of graphite and of/ Sf# /of monolite fast scarlet , whose particle else ranges are between 1 and $ microns* It appears that most lamslli- branohs are able effectively to filter small particles oat of water* MeOInitie (19U1) investigated the method of feeding in four Pacific specie e by observing the process through a glass window placed over an opening cut in the shell* He came to the conclusion that feeding can only take place when a sheet of mucus entirely covers the gill* He also maintained that because a bivalve is pumping It is not necessarily feeding, and the straining of the particles from the water currents by mucus is emphasised. It is interesting to note in this connect in , that Hopkins (1933) in discussing the marked changes in pumping rates observed in g,* glares, says (page 1*88), "It mey be also, a s suggested by G a lts o ff ( 1928a), th a t mucus forms a la y e r over the g ills, clogging the pores and impeding or stopping the current." In order to check McGinitie,s observations, s im ila r windows were made in a number of specimens of J[» uullaatra. Observations failed to disclose evidence of a continuous sheet of mucus over the g i l l , though It. must be admitted that, due to the transparency of the mucus, It was frequently difficult to decide as to its presence or absence* The ntroduetion of particles of a variety of slses into the inhalant stream always resulted In those p a r tic le s being conveyed over the gill entangled In strings of mucus and not in a ^ieet, Furthermore, the introduction/ 82 * /introduction of a coloured suspension airing pumping invariably resulted in the production of coloured faeces, indicating that, with these suspensions, pumping was always accompanied by feeding* The modification of Fox, Sverdrup and Cunningham1 a method used here was the replacement of the estimation of concentrations of suspended material by chemical means with one based on the principle of light absorption, which was later found to have been used by Jorgensen {1 9k3) , with a Rehberg elect rophotomster* The Instrument used here was the Spekker Abeorpt ioraeter which is a sensitive instrument recording quantitatively minute changes in intensity of colour* The normal procedure in using the abeorpt lometer is to develop a calibration curve by taking readings at various known dilutions of a solution or suspension of known concentration* However, since in the case of the suspension (jew eller's rouge) used in these experiments, a linear relationship exists between concentration and afeserptio

Experimental Method. With minor variations, the following technique wee weed in conducting the experiments* One gram of iron oxide woe added to two litres of filtered see water and stirred with a high speed electric stirrer for 5 minutes* This suspension was allowed to settle for 30 minutes to allow the larger aggregations of particles unbroken by the stirring to settle out* 1*5 litres of the supernatant fluid was then decanted off and made up to 3*0 litres* A deed clam, equal in else to the experimental animals, was used in the settling controls to make them and the experiments as comparable as possible, for It was found that, In stirring, some of the suspended particles adhered to the shells. Each of the experimental animals and the dead control had previously been placed in a litre beaker containing 500 cc. of pure filtered sea water, and to each of these was added 500 oc* of the oxide suspension to make up the experimental volume of one litre . The final concentration of oxide was not greater than/ 8 5 * /than 0*1 grams per litre , equivalent to 0*02 cc* of solid material per liti*e* The stirring apparatus was set in motion as the suspension was added to the beekors* This apparatus consisted of a 1w by perspex plate inserted in oach beaker to a distance of 2 inches from the bottom* The plates were rotated on thoir own axis by electric motor and pulley, geared down to approximately 90 R*l *H# » a speed sufficient to keep the main body of particles in suspension, but not. sufficient to lift from the bottom of the beakers the heavier aggregations that had settled out, or the strings of faeces and petmdofaeces* The purpose of the stirring is two-fold* First, to attempt to reduce the settling out effect to a mlniium, and second, to keep the concentration of particles homogeneous through­ out the suspension* I t the suspension wore not stirred the animal would, due to its own feeding activity, soon find ltsolf in an area devoid of particles, and this is a critic- ism that may be levelled against Jorgensen* e method In which no stirring was done* Three experimental animals, and one control, were used in each trial, and all four beakers were stirred and treated In the same manner* Reaulte from 26 individual experiments given In Appendix 1, were cbta ined using iron, oxide, 9 experiments were conducted with Monolite and 3 with Aquadag, as well as many test experiments and others that were abandoned for various reasons* Samples for *spekkerlng" were taken with a pipette, always from the/ / t h e m m pdai at mid-d^pth and m in ch from, the wall* fhe in itia l ©suapl© was taken iiaifcdXutely fcfter the stock rouge suspension had 'bean added, and from then on, usually at half hourly i>6riods fox1 intervals of 3 to 5 hours# For experiments 30 oe* samples v?oro token for use la tbs 30 cc« ^epekkow^ cell* A w^tex* setting of 1*000 was used with neutral filters* For experiments 16-ty), 8 ee* samples were token to use in 3 ec* "spokfcr*9 e e l l with a water setting of 0*2|Q0* A standard procedure was adopted for sa&pllng and '’spekkeriag” and this was rigidly adhered to throughout the experiments, so that the technique was standardised*

* gathowBUoal Treatment.

D o d g s o n (1928) used tbo tin* required to clear co m p letely a known volume of suspension for determining the rate of filtration of Sfel&aa sStiifi* *° a«*oaat was taken of the fact that the suspension was becoming progressively diluted, and with the progress of tim e , greater amounts of water had to he filtered to obtain equivalent diminution in the concentration of pert idee* However, he pointed out that the v alu es so determined were ffljaiaum ones*

m Hr* R« Barnes, M illport, assisted with the mathematical treatment which was further checked by Br* E*A* Robb, HetheraetieDepartment, U niversity of Glasgow* ST. It would appear that the process mlgtt he Interpreted by the mathematical concept of compound Interest with a negative slgnf using the following assumptions:- 1 • The filtration rate is constant* 2* All suspended material in the water passing through the inhalant siphon is removed by the gills* 3* The amount of suspended material filtered out is proportional to the concentration of the suspension present* On this basis f there should be a linear relation- ship between time and the rate of removal*

Thus i f : V— equals original volume in litres* a eq u als original weight of suspended m aterial* y equals ———- final weight of suspended material at time t« t eq u als time* r equals rate of filtration* P equals "speldcer" reading*

Bach time r/v of the amount present is filtered, the amount^ | x amount present j Is removed* y « a * e t

a v But the concentration of suspauded material la E x *epel&eg* reading* So t h a t :

B . S . P 1

jr * k . p 2

o r loge 8fj - f *• *-f 1080 (If)

The natural logarithm of the ratio, successive "spotter” to the original "spettsr" reading at time sere* la plotted against time to giro the filtration rate at which the suspended material la removed# Slnee the rate of remoral of suspended materiel in the experiments with lire animals is due to a corcfeinatlon of the amount actually filtered out by the animals plus the amount that Is settled out by gravitational effect, it is ueceerepy to estimate that latter amount# This was obtained from the control settling experiments, one of which was run in conjunction with three live experimental animals as described above# From the type of curve derived by plotting the amounts settled out against time, it would appear that the amount precipitated in unit time is pro­ portional to the total amount which is suspended, end equation 3 above can be used to describe that rate of s e ttlin g # 8 9 . Thae the actual rate off filtration hy th e anim al* can he expressed hy t

K ate F loge “ loge W 7 then loge |£f£j Is the tangent, of the curve deeorlhlng the rate of filtration by the animals, In which is Included the ►c settling rate, and loge is the tangent of the curse I®' describing the rate of settling to gravfation*

The data is first plotted as against time, and as 1n (P2®) against time* These curves are shown in ( p i *) Plates 28 and 29# In Table 9 are listed the logarithmic decrements for the first hour of the e^perlmextt both in the animal and the control experiments, and the rates are calculated from the difference between these two values and reduced to a unit of tins of one hour* On Plate 30 is plotted the filtration curve (lower line of long dashed), for Experiment 35, data in Appendix 1* The line of short dashes is a straight line fitted by the method of Least squares* The upper line of long dashes is the curve representing the rate of settling of the suspension, also plotted from the data of Experiment 35# Appendix 1* The filtration rote is obtained by taking the difference of the tangents of the 2 curves and modifying this by the time and volume ratio as indicated in the itlcn, page * S i M i *

S3B5F LogaritbiHo deoTaaent f lms ~msr X xperi a t ( a ln - l i l t re# m ental sxperi- Animal Control n teo ) Animals ■ JtefflBi..

0 . 0.3427 0.344 X1 0#i 0.1054 3.11 , 0.181 X2 1,3262 0.1301 1.1961 77 0.932 1 1.4024 0.1301 .2723 0.992 2 1.3280 0.1301 .1979 % 0.934 3 0.5863 0.2319 0.3544 60 0.354 1 0.4231 0.2319 0.1912 60 0.191 2 0.6632 0.2319 b.4513 60 0.451 3 0.5888 0.2263 3625 60 0.363 1 1.00S4 0.2263 60 0.776 2 0.7864 0.2263 60 0.561 3 1.1744 0.5159 0 .1 ^ 5 60 0.659 1 1.1394 0.5159 0 .6 2 3 5 60 0.623 2 1.41 0 .5 1 » 0.9625 60 0.964 3 0,1 0.3774 0.2072 60 0.207 1 0.75! 0.3774 0.3776 60 0.378 2 0.1 0.3774 0.1452 60 0.145 3 0 . _ 0.1143 0.5893 60 0.295 2* 3 1.1(077 0.1143 1 .2 9 m 60 0.647 1 , 11 0 .9 5 m 0.1143 (0.8431 60 0 .4 2 2 6 , 7 0.3302 0.1278 0.2024 60 0.202 4 0.5260 0.1278 0.3982 60 0 . 3 ^ 7 0 .4 2 1 6 0.1278 0.29! 60 0.294 1 0.1926 0.1878 0.! ' 60 0.545 8 0.9972 0.1878 OJ 60 0.809 9 O.652 O 0.1878 0«M»i 60 O .4 6 4 1 0

4 - Of * 30 as* sarapl# removed* 16 - 18 1 30 ee* sample removed ana returned# 32 - 40 s 0 ce* sample removed and returned# (a) 1 2 animals used in the one experiment# 90* Re cu lts * The graphs mi Plates 28 and 29 show the relation­ ship between the rate of remoral of the suspension and time* and the tangents of these linos ere the filtration rates* For the first 90 minutes this is a straight line relation­ ship: thereafter in a number of cases the slope of the line alters* This may be attributed to the fact that the rate of filtration has changed, if the original assumptions given on page 88 are correct* On the other hand the change in the slope !nay be due to these assumptions being incorrect, and the filtration rate Jigs remained constant* It would appear that the former conclusion is the more likely because in at least 50 % of the experiments the straight line * relationship holds over the whole period, and in nearly till eases for the first third* Also it is not unreasonable to assume that the filtration rate may be subject to Change, especially when the animals are in such an abnormal environment* Kelson (1921) found that ▼lrglnloe continued to feed under conditions of high turbidity, when the solid matter in the water reached 0*h grams per litre* As stated above, the maximum concentration of solid in the suspensions used in these experiments was only 0*1 grams per litre* Ho check was made on the possible changes In jfi, oxygen concentration, or carbon dioxide tension which Influence ciliary activity (Gray 1928)* In the relatively small volume of water, any one or a combination of these may/ 91 # /may have caused an alteration in the filtration rate* The rates found for £* oul^aatra given in Table f t v ary between a minimum of 0*11*5 l i t r e s t o a maximum o f i 0*992 litre s per hour, with a mean of approximately 0*5 litres at temperatures between 15 and 16° C* In Table 10 are given the measurements of the experimental animals with the average weight of 22*1 grama the filtration rate le found to be 0*0226 litres per gram per hour* In comparison with Jorgensen* e figure for J$* JBflaUS J* A® although too much emphasis cannot be placed on comparisons of this sort; first because of the difference in gill structure* and second because of the ten^ersture differences at which the experiments were conducted* As pointed out by Galt soff (1926* 1928} and Hopkins (1933) > the rate at which g ills pump water depends on the temperature which* in turn* affects other mechanisms such as the adductor muscles which control the else of the apertures and so influence the amount of water that can be moved* regardless of ciliary action* In Table 11 are given the filtration rates obtained by a number of investigators for various species* Fart of Table 11 is taken from Fox* Sverdrup and Cunningham (1937)* with the addition of the results' of more recent work*

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«■*» m o l • > Q F £ £ 0« g £ £. • » • * • • • £ i ?&3C s! s &s 8 S 8 8 i TABLE 1 1 . Filtration of' Water “by Plankton Feeders Average rate In v e s t­ Animal Method o f f i l t r . ig a to r p e r hour n er animal Grave O yster Plankton counts in 0*167 (1905) water and stomach Moore O yster Plankton counts in 1.25 (1913) water and stomach A llen Freshw ater Rubber tube in 1.1* (1914) Mussel exhalent chamber W ells O yster Plankton counts in 7.5 (1916) water and stomach Heeht A soidian Tube in 7.2 (1916) atrialsiphon Nelson Oy st er Rubber apron over 5 .7 A 26 (1921) exhalent area G a ltso ff O yster Rubber tube in 2 .5 -2 .9 (1928) exhalent charriber 24-26.9 0. Dodgson Mussel Clearing of 2.0 - 17° C (1928) (M vtilus) suspensions P arker Sponge Tube in osculum 3*2 (1914) Samas Cardium Clearing mud 0.1 (1935) suspensions Fox e t a l Mussel C learin g CaCOj (1937) H, californianuB suspension 1 .4 —6*4 Chemical analysis 18-20° C.

J orgensen Mussel Clearing algal (191*3) M. ed u lis suspension 0.15 „ E1 ect r ophot oraet r ic 11-22° 0. a n a ly sis

Loosanof A O yster Rtibber apron over 25-27. Nomejko exhalent area 19-26° C. Coe clam Not s ta te d (19h7) Tivella stultorum 2 .5 tt* /due to exhaustion of supplies of mucus from the g ills. To test this, several experiments ware arranged in which the animals had been pissed in a concentrated suspension of iron oxide for periods of from two to three hours previous to the experiment. During this time they had all pumped actively, as indicated by the clearing of the suspension. Experiment No. 34 is one of these in which two animals were used in the single experiment, the controls were Nos. 32 and 33. By examination of the graph on PI. 29, it Is seen there is no significant difference in the rates between experiments 33 and 34. In experi­ ment 32, one of the two animals was inactive. The animal in experiment 35 had previously been in pure water. The animals in experiments 36 and 37 were together in 2.5 litres of a concentrated suspension for three hours before the experiments end had nearly cleared this. There is no appreciable difference in the filtra­ tion rates of the three animals. In experiments 28, 29* 30, 31 * (PI. 29A), where the suspension was Agnadag "8% the animals in the last two had been placed in a concen­ trated suspension of rouge for three hours previously. The controls (28, 29) show a slightly higher filtration rate. Ho settling control was used for this group, but previous tests had shown that the initial settling rate of Aguadag *8* is negligible. The sharp drop in the curves after the 90 minute period is doubtless due to the/ /the flocculation of the graphite particles. In general, it would appear from the experiment a described above, and from other beets, that V. ^ullaatra is able to eecrete mucus steadily for periods up to six hours while filtering water containing large amounts of suspended material. In Table 12 is given the rates obtained from three animals which were used in five groups of three experiments. The mean rates of 0.51, 0.59, and 0.51 litres per hour ©how little difference, although over the five experiments there is a considerable range of rates for any one animal.

a i u i m * It is difficult to obtain accurate measuremente of g ill area owing to the extent to which the lamellae distend and contract, and from the difficulty of removing all the gill tissue from the body mass. The experimental animals were anaesthetised and the gills dissected out with all possible care. They were then placed on a slide and the outline projected and enlarged on squared paper. Attempts were made to measure the areas with a plan!meter, but the method was discarded owing to wide variability in results. Counting squares gave reasonable accuracy and the average g ill area of the experimental animals was approximately 40 square centimetres. With a filtration rate of 500 ee. per how, one square centimetre of g ill is capable of filtering 12.5 ee. per hour. It would be interesting to/ Anlaal 1. 2. 3*

Bates la Litres 0*93 0*99 0.93 p e r hour 0.35 0.19 0.45 0.36 0.78 0.16 0.66 0.62 0.96 0.21 0.38 0.19 0 .3 4 iv«fi|* Bate 0.51 0.59 0.51 /to know whether all parts of the gills are equally concerned la filtering or whether the "ascending” lamella of the outer demit*ranch beers the brunt, for in observing the g ills through a window, the demibranchs seem to approximate very closely to each other and to the visceral mass* Careful comparison of the histological structure of the various areas of the gills m y reveal a differential development, for Hldevrood (1903) has pointed out variations implication in different areas of the gills, for example, la the number of filaments in the plicae* Ho mention is made of function in relation to these variations*

Current Booed. Considering the siphons as tdbes, the moan velocity, 3m, of the whole sectional area of the siphon is half ths velocity at the axis and the rate of discharge, ?#i in ee* per second is : (Cibson, 1925, page 63; after Oalteoff, 1928), The mean diameter of the exhalent siphon of ths experimental animal is 0*3 cm, and substituting in the above formula, the velocity of the stream at ths axis, using the discharge rate of 1,000 ee* per hour (the maxlmon value), is found to be approximately 8 cm* per second* The mean lnhalent aperture Is 0*5 cm* when pumping, and substituting again the axis trap rent speed is found to be approximately 3*0 cm* per second, which is only J the speed of ths exhalent current* This represents an adaptation for/ /fo r discharging the excreta and de-oxygenated water ee far as possible away from the inha lent aperture* Coupled with this, is the pronounced divarication of the siphonel t i p s , th e minimum an g le between them when a c tiv e le 90° * The inhalant siphon is usually directed vertically, while the exhalent is directed backwards in the direction of the animal itself and approximately parallel to the surface of the substratum* This bifurcation must be a great aid in separating the inhalant and the exhalent currents.

Difteuqa^oiu The results of this section of the work are in rase ways preliminary, for while clear information about the rates of filtration of adult animals has been obtained, this applies only within a limited range of temperatures and of else* Further experiments enlarging these ranges would be of velue end would contribute much to an assess­ ment of the reliability of the results* An examination of Table 11 ehows the wide rang© in filtration rates that have been obtained by various investigators* The range is so great that one la at a lose to decide even within broad lim its what values may consllute reasonable estimates* Co^arlsons ere made difficult because of differences in sixes of the animals used, as well as in the variety of species, and in the wide range of temperature* Galtsoff (1928) used two methods for comparison, but the basis principle underlying both methods is open to criticism* 96 * The result© of Fox, Sverdrup and Cunningham (1937) appear to be sound on a comparative basis* The mala criticism of their c&thod is the high concentration of the suspension, abetct 3 grams of calcium eertronat* per litre , which is much ©bora normal* Kelson states that very tuibid water, natural in Barnegat Bay, contains only 0*U grams of dry material* Estimates of normal water at La Jolla, California, place tho dry material at 0*05 grams per litre* Jorgensen* s use of the electrophot ometer is an advance, but the use of algae has its disadvantages* The cultures must be fresh and since large quantities are necessary, a proper supply would be difficult to maintain* It is also possible that numbers, end therefore the colour, may very during the course of an experiment* Tho work o f L oosaneff and Hotnejfco (19M») appear* to be sound, but mean values of 25 to 2? litres per hour seem extrem ely high* Goe (i9Ul), on what evidence he does not state, estim ated t h a t a Piemo dam (give 11a m tvU to m m ), 7 0 ora* long, filtered 2*5 litres per hour at La Jells* At this rate it is capable of obtaining about about 0*3 grams of suspended materiel per day, though only a small part of this may be swallowed end digested* On the other hand Coe believes that the daily requirements of th e clam are v ery small except during garnetogenesle, because the dry organic matter in a clam 70 na* long, end ©bout th re e y ears o ld , is only 1*5 to 2*9 grans* On this b a s is , b specimen of Pet res virginica* four inches high, lw / 9 7 . /Is claimed to filter at least 25 litres per hour (Loosanoff md Home jko, 19^6) and should he able to obtain 3 grams of potential nutriment daily, which is roughly equivalent to its own dry body weight, Xf previous estimates of the filtering efficiency in marine Invertebrates have been too low, this would explain the disparity between the nutritional needs indicated by oxygen consumption and the supply of food based m e s t i ­ mates of filtration# Comparative filtration rates per unit of weight of other epeoleo, such ae Mytllue oallforalanua. indicate that the rate found for 2# oullastra is somewhat low# The rate is comparable to that given by Coe (19U7) for the related Flsmo clam# Also the temperatures of the experiments here described were rather lower than most of those quoted# What is needed is a comparative study of a mnfrer of species and it is believed that the method developed here provides a relatively rapid and accurate means of determining filtration rates# But owing to the limitations of this type of experiment, the results will not be more than good estimates of the true values# The pressures set up in 2# nullsstra by the water currents are difficult to assess because of the c o m p le x route taken from the inhalant siphon into ths p e l l i a l cavity, through the gills into the supr&branohial cavity and out through ths exhalent siphon# However, because of the low filtration rate, it may be assumed that/ 98. /that the pressures are low and it is doubtful if they play any part in the spawning act# The speed of 8 cm# per second agrees quite well with direct observations on the speed of particles such as clumps of eggs leaving the exhalent siphon# The gametes are carried as much as 15 cm# from the siphon in undisturbed water, although this distance varies a good deal and spawning animals have been observed in which the ova merely trickled out of the siphon, end sank immediately to the bottom# This is another possible indication that the rate of water propulsion is not constant even under identical physical end chemical conditions# 99# S h ell Movements. A considerable anount of data on the shell movement© and their significance in the physiological activities of various specie© of oyster© now exist# See G a ltso ff (1928), Kelson (1921, 192i*, 1938), and Loosanoff and Nomejko (19*|6) on Octree v ir g ln lc a * Hopkins (1931) on £• lurlda: and Webb (1930) on £• e d u lls * On other lamelllbronchs the research of Loosanoff (1939, 19U2) on M ytllus ed u lls and on Venus mercenaria are the only papers known* The primary purpose of this brief examination of the ©hell movement© of Dullestre was to determine th ese for eomparison with movements oecurring during spawning* However, when the spawning season arrived, i t was soon observed that s h e ll movements played no significant part in the spawning act of either sex, as is ths case with the female of several species of oysters# nevertheless, one or two points of interest have arisen from an-alysis of the kymograph recordings of the shell movements* To make the condition© ee natural as possible the recording apparatus was set up so that the animal was buried in the sand in a natural position* The apparatus is shown in PI*31 • A block of sealing wax fBf i s attached by two metal pin© to a lead weight *Af * The clam fCf Is attached to the sealing wax by one of the valves and a perforated perspex pin is connected to/ 100. /to the posterior end of the other valve. This part of the apparatus is buried in the sand of the aquarium, with the posterior end of the clara just below the surface of the sand. A ©olid perspex lever with no whip in it i s swung from a hinge at point #Ff • The hinge arrange­ ment is attached to a heavy adjustable weight fGf* A length of stiff brass wire *Df connects the bottom of the vertical lever at 1 1 to the clam through the p e rt oration in the perspex pin. The recording pen ,JKf is connected solidly with the vertical lever *1 Jf, and the whole hinged at point fJf. 11 K* is a light connecting rod Joined to *IJ* and f^llf by hinge connections. When the clam opens its valves, it w ill be seen by following the lever system, that, the recording pen r is e s . The tem­ perature in the aquarium was thermostatically controlled. A series of experiments at low t emperatures would have been desirable to round out the investigation, but no equipment was available to maintain them for an extended period.

A criticism that may be levelled at this experi­ mental procedure is the fact that the animal is in an aquarium and subject to the composition and v a ria tio n s of stored sea water. On the other hand the animal was in a perfectly normal posit ion. Loosanoff (191^2) was able to keep his specimens of Venus riercenaria in large tanks which were connected with outside sea water and in which the natural tidal fluctuations occurred. However, his clams were cemented to a block by one valve and were/ /were consequently lying cm their ©ides; an unnatural position. It is diff icult to estimate how much a lateral position may interfere with the disposition of material accumulated in the mantle ohonher. A contoina- t lc u o f Loosanoff* e method and the one used fo r J . oujlastra would have been ideal.

R esu lts. Approximately 300 hours of recordings were mode over the temperature range whose lower lim it was governed by the temperature of the laboratory circulation system and the upper limit at what was considered the maximum the animals may b© subject to in nature. Photo­ graphs of eome of the reccrdings are given in Plates 3 2 , 33 and 3h* In Table 13 is given the analysis of each recording and below is given a summary of that analysis, 8nmETO nf »*■"»•« trm the Analysis of Recordings. 1. The shells of jr. nullastra remain open nearly 100 % of the time at temperature between 15.0 an. 22.0° C. 2 . S hall movements are frequent; end they

have e mean amplitude e q u a l to half the maximum distance to which the valves are opened. 3 . The clo rin g movement i s rapid end the following opening movement is almost instantaneous, although In the final phases of opening the movement slows down. Qwamvy of Analysis o f Kymograph Recordings of_3he.il Movement*

AT. Ho. HO. Day o f o f Sura % .ot ef and - - * ~ S ate a n i ex Temp. Range tio n tim e d n U Htyttai UMiC Temp. tael post degrees C. (Hrs) open ex pen effect «®jot e la n

30.6.1i£ A 1 15*0 19 190 Ffc* n i l B 1 5,0 _ 19 199 M l _ n i l M l__

. 2#7#ii6 P k n...1 6 .3 1.... - ,3 19® «9 Fee. _M l M l 2.7.U6 ..33 - 3 - .1.6*5...... 199 89 n i l _ n i l i U.7.li6 F i% 21 ftp — .22*5 k 100 99 700 M l lu7.itfi 0 HP 19*0 ». 21*0 ,_k_. 199 95 n i l

ii/5.7.W 5 F h a 1 9 .0 - 2 0 * 0 9 199 95 n i l n i l n i l Ii/5.7.1t6 9 11P 19.0 - 22.0 9 109 75 7«0 n i l 5*7.U6 F 12A ia * 7 ~ m * z # 109 90 n il n i l M l 5*7*li6 0 1W 22.8 ~ 20.6 9 199 99 m , n i l M l...... 5*7.h6 F 13A 18.0 - <€*€ 5 t 199 75 ML 5*?*h6 0 12P S i 199 90 70ft M il M l ^ 6 -7 .ij6 F 16.5 - 15.1 9 109 59 xee M l 5/6.7.U 6 9 1W 18*5 — 16.0 9 190.... 75 Fee F 15A 15.3 - 1 6 .0 9 0 11* 16.0 * 16.5 9 109 80 Fee n i l n i l ' 8 .7 .ii£ p t # ,17.0 - 17.lt I t 199 69 n i l n i l n il —it J 17.lt — 13,0 99 1*5 Fee n ^ l n i l 8 .7 . ij6 1 17A 19.0 - 21,4 7 100 n il M l n i^ 8 . 7.1*6 J m 4 3.7 - 21.2 7 100 n i l n il M l TABLE 1 3 .

auBWMOr a t Aaalyala o f K:m>fa*>Efa Keoordioga of Shell .KaranM&a

"At . Ho* Ho* OB0NO Day o f ode— .a D ora fUot ©f and S a te a a i ex £eag>. Range ^ io n tim s h e ll a y tm xd&xt Temgb 2m l gQPt d e g re e s C . open expan COBQS aCCtoet meat s lo a S5.. a /q .7 .ii6 1 29.0 - 23.0 ft a l l a l l n i l 8 /9 .7 .M f 8 n i l n i l n i l .... 1 0 .7 ..W ft 19A 21.3 - 20.3 17 199 05 yon a l l n i l 10.7.146 19P 19.5 - 21 .5 13 190 T a l l «*t 1U7.U6 St 1 8 .5 199 y©s- n i l n i l 11>7«b6 I . 2 ® 1 8 .5 ... 71 tpo a l l n i l M /4 2 * 7 .ttS W 1 8 .0 _ 9 190 90 M i . n i l n i l u 1 8 .0 ft 190 60 mm a i l n i l «so_ 12»7*b£ P .$£•$.<**. 19*5. nT.rff 190 85 ..y e a n i l n 't! _28 . 12.7.1*6 M M 18.5 - 19*5 If 199 99 y e a n i l n i l . 1 2 /1 3 .? .l£ If .....ft.... 99 _ 98 ... mm n i l

ISObZittl JL ...A2.nl..,. . m L_ s s l J iL .JSiLm 102. km The degree of separation of the valves over the period is nearly maximal. 5* There appears to he no correlation between type and amount of shell activity and temperature over the range investigated. 6m Changes in tenv>erature, positive or negative, over the range investigated, had no apparent effect on shell movements. 7. Presence or absence of light heve no effect on tho period or degree of separation of the valves or on general activity. 8 . Shell movements may be deeslfied as being associated with digging, cleansing or random activities, but none of these is associated with any characteristic Kymograph tracing. 9. Some anim-le show a definite rhythm in their shell movements at one time and not at others. Individual animals may have a rhythm peculiar to themselves. 10. There may be considerable siphonal activity; opening, closing, extension or retraction, without any correlated shell movements.

Dlseusaloa. In Pl.32, fig.1, is eh m n a tracing of the shell movement o of J . o u lla s tr a a t a tem perature range of 16 to 18° 0* On the bottom of the treeing may be seen the base line which marks the position of the recording pen when/ 103. /when the valves are closed. Over the period of k hours and 50 minutes covered by the photograph, the shell is never more th an h a lf clo sed . Opening movement s a re very rapid. Approximately every half hour there is a period of no shell activity (indicated by the horizontal unbroken line) with intervening half-hourly periods of activity. A certain rhythm of shell movements is evident although It is difficult to determine the border­ line between rhythmic and non-rhythmic movements. While the closure baseline is not shown in every case, most of the tracings indicate that the valves are open practically all the time# An exception to this may be seen in PI.32, f i g . 3 . where, for a period, the tracing touches the closure baseline. Loosanoff (1939) found that Venus remained open 69 to 90 f of the time over e twenty four-hour period at a temperature range of 11 t o 27.9° C, while between 21 and 22° C they remained open 90 % of the time. Nelson (1921) found Qetrea Virginia* to be active 20 hours out of 21*.# while G sltsoff ( 1928 ) found the same species was active for only slightly over 17 hours out of the 21*. Hopkins (1931) found a diurnal v a r ia tio n in th e amount of t i m £• lurida remained open, but that this could be directly correlated with the fluctuation in temperature, even though the mean variation was only 2.1° C. He found the animals opened for 50 $ of/ 10it. / o f th e Item at the lower end of this temperature range, end f o r 95 f a t the upper and* Loosanoff and Homejteo ( 19246 ), working with £. vim laica found that It remained ©£ea f o r 9km3 £ of a 2h h ur oeriod within a temperature range of 17 to 26° C* Thus it api ears that over s temperature range of 15*0 to 22* 5° c ., I . jM&J&ES remains open longer than either jM m YJUrfftelfi& <* YSWB. raareenarlpt also comparison of the tracings for this species with those published by the authors cited above indioat ee that J> puHastra is considerably more active on the basis of frequency of Shell movements* There appeared to be no correlation between temperature and the amount or type of shell activity in X* ©©,11 * etra* nor did changes In temperature have any effect* Hopkins (1931) believed that it is the rote of change of temperature rather than the amount of change that is significant in causing variation in the amount of shell opening la Oatrea lurida* Gaits off ( 1928 ) believed that £• ylrftlnfea tended to keep its sheila open ae long as possible and could find no correlation between temperature and opening and closing within the temperature ra n g e of 13 to 22° c* Kelson (1921) concluded that £* vlgglnlea tended to be less active during the night than during the day* and that th is species feeds Xesr^act ively during the ebb tid e * Both L oosanaff and Nome^ko (192)6) end G a lte o ff ( 1928 ) fo r 0 . virgtniea appear to have disproved both of/ 105. /o f these contentions and, in addition, Webb (1930) found that there was no difference in the activity of the adductor uscle of £• edullo between day and night* Loos an off (1939) found that Venus mercenarla was closed for somewhat longer period© in daytime than at night* Ho such effect was found for 2* nullastra which showed a tendency to stay open as much as possible, regardless of the time of day or night or of temperature* Galtsaff (1928) pointed out that partial closures of the shells SI* vlr; in^ca may occur without rejection; also periodic contractions of the adductor muscle* This also occurs in J* oullastra* The periodic nature of some of the contractions has been indicated on the photographs of the tracings* Repeated observations showed that only at infrequent intervals did shell closures or partial shell closure coincide with rejection* Hopkins (1936) was able to analyse into three groups the movements shown on kymograph recordings of the shell activity of£ . sclaae: those involving discharge from the branchial chanber, others concerned entirely with the oloacal chamber, usually resulting in the discharge of faeces, and a third type which he terms non-specific, which may be due to a variety of causes* In J* pullastra the adductor activities have been classified as being associated with digging movements, cleansing, or random movements* A comparison between Pl*3h, fig*3 showing a/ /a tracing of digging movement** (this should be viewed upside down for comparison) end of any shell closure tracing, ©hows little fundamental difference* I t has been pointed out that the tracings resulting from the rejection of ©olid oiaterial are identical with those in which no discharge occurs* Ho doubt many of the partial closures are the result© of attempts to carry out digging movements* Hopkins (1936) in analysing the random contractions in £* nigas finds no correlation between their frequency and temperature over a range of between 2 to 30° C. and believes they may be traceable to some external stimulation such as light, vibration, suspended material in the water, or to an accumulation of secreted mucus* It would appear that this explana­ tion is hardly satisfactory, especially for 2* nullastya. when so many of these movements are periodic* m .

The object of this sect ion of the work was to determine whether there exists in 2* csllawtrs & sti&ulus which initiate© spawning, as there is In other marine Invertebrates# G altsoff (1938a, 1938b, 19V>) in extensive woartc on the physiology of spawning of Qetrea Virginia* and on 0. fgjgss found that there m y be several "critical* to^eretures for spawning, different for male end female* These temperatures are partly determined by the physiological cadditions of the animal* Oeltsoff also showed the import­ ance of chemical stimulation in the initiation of the ! spawning act and that this lowered the "critical" tempera­ ture* Grave (1927) mads the statement, "Spawning is caused at particular times in nature by various specific stimuli and Is suit determined by temperature alone*" He believed that shock or the mere removal of Cnmingis tdlineidftg into the laboratory was sufficient to stimulate spawning and that spematosoa did not stimulate the female to spawn* Morgan (19111) believed that the presence of sperm in the water incites female £« to spawn mare readily* Chemical stimulation has been described for several species of chitons (Heath 1905) » for Here is Mifcittt (U U ie sa« Juat 1^3) ma for atrongrlooentrotao nwtoam {rat 192*)* BXoasr (1936) wo otae to taring about artificial stimulation of spawning of Qstrea gjgss on a la r g e r sc a le in Ladysmith Hazfeour* 108* Methods* During part of the time no thermostat control wee reliable so the temperature was regulated manually* These experiments sere carried out m breffit jars and the temperatures were adjusted by the addition of water* When a thermostat became available battery jars were used* The lowest temperature that could be controlled was governed by the temperature of the et ored se a w a te r used in the circulation system of the Marine station; therefore most of the experiments were carried out at temperatures considerably higher than the animals would experience in nature* However, the temperatures appeared to have no harmful effects* The aquarium water used in the experiments varied between 12*0 and 16* 0 ° 0* and wae filtered to avoid contamination by sexual products which may have been present in the normal supply* Egg and sperm suspensions of approximate concentration 1*0£, from the gonads of 2* mOlestra* were used* Animals were prepared for connection to the kymograph by securing one valve to a glass slide with a mixture of bitumen and pitch* With the same material a wire hook was attached to the other valve* The glass slide was held to the bottom of the tank by a weight, end the hook was attached to a vet leal lever, which in turn moved the hinged writing pen* Opening of the valves, caused a downward tracing* t<9« The animals were stimulated in the following way* « 1* A gradual rise in temperature with and without chemical stimulation (egg and sperm suspensions)* 2* An initially high temperature with and without ehemieal stimulation* 3* normal water teiaperaturea with and without ehemieal stimulation, the latter ©erring as a eontrol in ewery experiment*

Snanlng of tha Mala. Xn spawning a fine stream of sperm, not more than 1*0 ian* in diameter issues from the centre of the exha lent siphon* The stream maintains its identity for a distance of about 3 or k cm* and then begins to spread* The sperm may reach a maximum vertical distance of 15*0 cm* from the siphon* Spawning is not necessarily continuous, the longest time a male was observed to spawn was three hours* A small nmtoer a t observations indicated a refractory period of between two and three days* Caltsoff (19U0) found no refractory period in male Oatrea viiMiwiftB. which could be stimulated repeatedly until the animal became spent or fatigued* The adductor muscles pier past in the spawning act of the male X* nallastra. but during the period of spawning the adductor muscles appear to be less active than normal* 110. Qnmtox 9f fwntiit The spawning of the female is not unlike that of the male and a steady stream of eggs issues from the centre of the ©xhalent siphon* The stream does not extend as far as that of the male due to the difference in density between sperm and eggs* One female was dbserved to spasm the eggs in clumps of approximately 1*000 each* These trickled out of the siphon and sank immediately to the bottom* Sampling and counting disclosed that this female spawned a million eggs in 30 minutes* Smear examination of the gonad immediately after showed no evidence that the animal had spawned and this indicates the ears that must be taken in using the condition of the gonad, other than by examination of prepared slides, as evidence of the breeding condition* As with the male there appears to be a refractory period of two to three days after spawning, during which the female eamot be stimulated* ©eltsoff (134©) found the refractory period of the female Oat res vlrwinlea to last from two to five days*

Rmmmwr of Kxrerltaenf w ith PQGltlYe Beoolta. Zn tlie ounaor of both 19W> end 191*7 a series of experiments were carried out using temperature and egg mad sperm suspensions, individually and confcined* Zn no t more th a n 2© % of the experiments were positive results obtained* Attempts have been made to suntnarlse/ f t u /summarise th e m in table fora, but no satisfactory method could be devised, eo some of the pertinent data la listed below* May fSths At a temperature of 10*5* C*» SO minutes after the addition of a sperm suspension, a male spawned* The temperature bad been raised from 13*3® 0» during the period o f 1 hour* June 1$th: At a temperature of 20*5° C*, 290 minutes after the addition of an egg suspension, a male spawned for 1§0 minutes* The temperature had been raised from 15*1° C* during the period of 7 hours. JUne 19th* At a temperature of 16*0° C., a male and a female spawned with no stimulation other than a rise in temperature from 15*0° 0* during the p e rio d of 1 hour* June 19th: At a temperature of 20*0* C« , a female spawned 05 minutes after the addition of a spasm suspension* The tee^perature had been maintained at 20*0° 0. during the period* June 19th* At a temperature of 20*0° C*, a male spawned 115 minutes after the addition of a sperm suspension and 30 minutes after a female had spawned in the seam vessel* The tenpereture had been maintained at 20*0° 0* daring the period* JUne f9th* At a temperature of 20*0° 0*, a female spawned h hours after the addition of a sperm suspension sad 150 minutes after a male tod spawned i n / 112* /in the asm© contain©?* The temperature had hem maintained at 20*0° C. daring the period* June 19th* A male and a female spawned € hours efter being placed in water maintained at a temperature of 20*0° c* June 20th: Two female mad a male spawned 40 minutes after the addition of a sperm suspension# Within a ftow minutes of these* approximately 15 animals of both sexes began to spawn* The temperature was maintained at 20*0° C# from the beginning* June 22nd: At a temperature of 23*0° C#» a male spawned 20 minutes after a mixed suspension of egg and sperm had been added* 10 minutes later 2 males , and 2 females spawned* The temperature had beam maintained at 23*0° c* from the beginning* June 25rds 5 males spawned 4 hows after the addition of a sperm suspension* The temperature over the period was 20*0° c* June 25tht At a temperature of 20*0° C** a male spawned 47 minutes after the addition of an egg suspension* The tmqperature had been maintained at 20*0° 0* during the period* Jt&y lets At a temperature Of 22.0° C.» 2 males spawned after periods of 16 and 35 minutes respectively. The first spawned for minutes sad the second for 90 minutes* 113* July 1st: At a temperature of 22*5° C** two p re v io u sly spawned feraele ©pawned 40 m inutes a f t e r the addition of a sperm suspension* July let: A male spawned 90 minutes after the addition of an egg suspension* The tesparature tied been raclntalaed at 22*00 0* for 5 hours* July 2nd: At least half the animals in a group of 100 kept in an aquarium at a temperature of t€*0° C* spawned together, without any applied at inula- tiem* The smallest female found spawning was in its fourth summer with a length of 2*3 cm* The smellost male found epawnlng was in its third summer with a length of 1*9 em» On $&y 7th* a female was induced to spawn and attached to the kymograph* While this was being dens the animal was out of water for about 15 minutes* yet it continued to spawn as soon as it was replaced* The kymograph treeing of the valve movements of this spawning female is shown in Pl*35* flg*3* At first there was ©onstdevdble pedal activity which appeared to be quite independent of either the spawning set or of valve movements* At 14*44 hoars the shells were caused to close by stimulating the siphons in order to test the working of the kymograph pen* On Jttly 9th, a female was found spawning in the aquarium at a tengjerature of 16*0° C«, and it wa%/ 114* /m m tame&lately connected to the kymograph* The recording i® shown in PX*35, fig*5* At 18*58 hour® th e m*&m 1 was opawning Vigorously,, On July 11th, after a latent period of 3 hour®, at 20*0° C*, a male began to spawn# After a further period of 15 minute® a female began spawning and this animal was connected to the kymograph, the recording of ia shown in Pl*39, flg*1* AT 19*32 hour®, point x, spawning was under way* At 21*10 the temperature was 21*0© C* and spawning was coupleted at 21*30 hours* On July 12th, the activities of another spawning female were recorded and this is shewn in PI* 55* fig*4* The main spawning period occurred between 21*10 and 22*25 hours, and th is animal shewed more activity than the average during the spawning set* Prom these few recordings, however, in addition to numerous direet observations of spawning females, activity of the adductor muscle has been shown to play no significant part in the spawning act*

piSCUBBiCHU Ho definite quantitative conclusions may be dram from the above experimental data# However, it does appear that £* tmllastra la susceptible to both ehemieal end thermal stimulation, although the latent * period le often long. The twee spanning* In the aquarium also Indicates the presence «f s owbmb spanning/ 115* /spawning stimulus, and points to the sex products as being the most likely cause# It has been suggested by Thorson (i94&t page 424)» based on the fact that there appears to be a correlation between the breeding season of various invertebrates and the amount of phytoplankton p re s e n t, th a t t h i s may be th e spawning stim ulus# He supports this conjecture by citing the works of Mlyesaki (1936) on the use of algal extracts, such as from Plvs# for stimulating spawning in the males of 0etnas glass# Orton (1936, 1937) points out that gravid individuals are sensitive to variations in oxygen tension and that this may be a spawning stimulus# daltsoff’s (1936, 1939, 1940) work, stimulation by means of sex products and ether chemicals combined with temperature, has already been quoted# That some means is required to Induce simultaneous spawning in lamellibranche such as £• otfliafltra is unquestioned, and It remains to find the exact nature of the stimulus# The above staple experi­ ments have indicated that chemical stim uli, especially in combination with tenq>erature, are effective within lim it s# Compared with the ease and certainty with which Galtsoff (194©) and others were able to stimulate spawning in Oftgei vlrginles# as well as the author9 a own experience with £• gjgae# j , pullaatra is not very susceptible# Whether this Is a reflection of the reaction of this species to life in aquaria, or whether it indicates more exacting requirement8 for stimulation, Is not known# 116. Seasonal Gonad Changes. Zn connection with the determination of the breeding season and its relation to temperature and other physical fact ore, it is of interest to follow the develop­ ment of the gametes which involves the study of the seasonal changes in the gonad. For oysters such as £• gjgas, after spawning, a period of fattening ensues when the glycogen content of the body mass greatly increases. This "fat" condition exists throughout the winter until the late spring, when the increase, presumably of tea$>era- ture, causes proliferation of the dormant gonad tissues and gradual replacement of the "fat" by the sex cells, until the largest part of its mass is occupied by the gonad. If, for some reason, spawning does not take place or is incomplete, the residual sex cells are usually resorbed and converted into glycogen. This cycle is not followed by other species so far studied; such as Teredo navalis (Coe 1936), Venus msrcenaria (Looeanof f 1937) * Mvc arenaria (Coe and Turner 1938) and Pauhia st amine a (Quayle 1943)* A comparison of the sexual conditions in 2* uullastra with those of other animals which have been studied may be of interest.

Methods. Samples of 50 adults from the same area were taken each month throughout the year. The series was started in May 1946 and carried on until October 1947/ 117. /October 1947, during which a to tal of 923 animal® were examined# In this way, a complete annual cycle, with an additional breeding period, was followed# A sample of 50 animals monthly is not many for a study of this nature, and represents the minimum that should be used, but larger samples could not have been dealt with because of the time required in the preparation of slides. A sample of gonad tissue approximately 0#5 cm# square, was removed from the mid-region of one of Hie sides of the visceral mass and fixed in Bouin for 24 hours. The ester wax eobadding technique (Steadman 1945, 1947) was used exclusively and found to be most satisfactory. All section© were at first ribbon stained with methylene blue end mounted immediately without counter-staining# The only operations after the sect ion© had dried on the s lid e , was the removal of wax end mounting in balsam . This gave all the details necessary for an accurate deter­ m ination of th e s ta te o f maturity of the gonad# As the slides were being assessed, those required for detailed study, drawing or photography, were noted# The ester blocks having been numbered,further sections were cut and stained with other methods such as Heldenhain. This latter stain alone gives a clear picture of the gonad tissue and even the thin walls of the follicle cello show up clearly# In a description of the seasonal changes in the gonad, the inmedia te post-spawning period is the most/ 118* /moat suitable starting point because then the female b eg in s to develop* Since most of the spawning is completed by the end of Septentoer, that month may be chosen as a suitable starting point*

f In normal years rao^t of the animal© are completely spawned out by the middle of Septenfcer, though Isolated Individuals m y show evidence o f having only p a r tly spawned as indicated by the relatively large number of residual mature ovocytes, whereas those animals which may be described as "spent" contain only a few ovooytes in the otherwise empty and collapsed follicles, (Pl#37» flg*1) • By this time, however, animals which have spawned earlier in the summer hove their alveoli filled or partly filled with follicle cells (?1*37» fig. 1) which ere relatively large cells, most often with a thin layer of peripheral cytoplasm enclosing a vacuole* From the description of Coe and Turner (1938), the follicle cells of ftyfB arenaria and £• pullastra are very sim ilar, except that the inclusions found by Coe and Turner in J* srenarla have not been observed in £* aullastra* They escribe a nutritive function in the follicle cells and this explanation appears to be likely in the case of J[* oullastra. for in both sexes the first development after spawning is the formation of the follicle cells, and their later disappearance coincides with the development and ripening of the gametes* Thus the period of follicle cell formation may be described as/ 119# /as a recuperative period* During this period there appears to he m m development nr avogonie and hr the middle of October smgr of them have become ofoeytH with a diameter of 35 xu (Pl*37, flg*h). By the middle of Hovenber# nearly all the alveoli are filled with foU iele sells and the ovocytes vary between 20 and 40 t» In diameter* Residual ova are still present and do not appear to he undergoing eytolysls (Pl*37# flg*3)» Development oontinues slowly during the winter# as shown hy the insreesed else of the ovocytes which average between 40 and 45 a* by the middle of February (Pl*3$» fig# 2)* Development now seems to be accelerated for* by the middle of April most of the animals sampled are ripe or nearly so* although a ftw are stU l developing* By June practically all are fully ripe with the tubules extended with ewooytes approximately 55 u* In diameter# The follicle cells have disappeared# initially la the centre of the lumens# as the ovocytes increased in else and number* until In the ripe animal there are only single peripheral layers# or In some eases only single Isolated follicle sells* The ovocytes* at first flat against the germinal epithelium of the tubules, assume a pear-shaped form with the thin stalk attachment on the follicle wall as they grew and develop* On becoming ripe they are detached and occupy the M itre of the lumen (Pl*36# figs* % 3 , 1*.) • Bxt*rn»lljr* the ripe ralrals *pp*ar plump rad OTea*r « h ttein Mtoor* A faXOjr rip* ralral l* raa# *«/ 120* /to identify, but the Intermediate etagee are mere difficult, even with smear examination, the seeti a m e re necessary far an accurate determination of the condition of the gonad* The June 19M> sample contained a nuriber of entasis dildi were spawned or partly spawned* hut no spent animals were found in the June 1947 sample* corroborating the evidence from the plankton hauls that izftlal spawning in the latter year was about one month later than In 194&* In this connection* it must be remoofeered that populations from different areas iaey spawn at different times and It Is this point which, no dotfbt* partly accounts for the long breeding season* The July samples shewed that the bulk of the population from the Cross Houses Beach had spawned end were in the recuperative stage* Varying Mounts of residual ovocytes were found in most animals, the amounts varying even between different follicles in the same animal* Briefly then, the cycle for the female Is cue of recuperation followed by proliferation of fe&liele cell tissued Immediately after spawning* Almost simultaneous with the proliferation of the follicle cells is the development of the owegcnla into ovocyte* and their slow growth during the winter months* The higher spring temperatures seem to bring on* or are at least coincident with, an acceleration in the development of the gonad, culminating in maturity in Hay or June* The spawning process has been described elsewhere, but it may be noted/ /noted here that in eoatxm with the finding of holding (tfffi) and Coe end Turner (1939) for lira arcnarls* the ova of 2* JSUsgSSS cannot be artificially inseminated « d 0 8 « ©pawned n a tu ra lly through th e oviducts* The fate of the uaspawned or residual ovocytes of J, pal lustra is uncertain* Ho evidence of eytolyels has been observed according to Coe and Turner (1959) * is shat happens in lira arsiuarla* Loosanoff (1937) is inclined to think that the residual ova in Venus gaercenarla are also spawned out by the and of November* such spawning being carried cm at interval© after the main oojmaei? spawning has been finished* Orton (1935) found a similar prooesa in Ootrea sdalia* Since in £• oullaatrs no evidence of cytolyeie or resoxbtion ha© been observed, rad from the fact that morphologically mature ova my be found in sons gonads throughout the winter up to the time when the new orop becomes mature* it may well be that these rellet ova w e spawned along with the new ones* though whether or not they may bo fertilised is problematical* Another argument* too, la that these mature appearing ovs|u©ually form only a smsll percentage of the ovocytes present until March or April* However* with the present evidence* the fate of the unspawned ova remains in doubt*

Males* The male cycle is not unlike that of the ffemle* The bulk of the males are also spawned or partly spawned/ 122* /spawned m l by the middle of Septea&er and eras are ha the recuperative stage la which the follicle cells proliferate rapidly* Zn only a small percentage o f th e laalee is spawning complete with the lamina left devoid of sperms (Pl*39, figs. 3 and 4)* There l e much v a ria ­ tion, but on the average, about 10 to 20 $ of the operas are retained (?1*39, fig « 2 )* When th e p ressu re e x e r te d by a fu ll complement of a perms io reduced by spawning, the remaining cells in the follicles are arranged in columnar and circular patterns, as shown in P I*38, flg*2* Development of the male sex cells after spawning la apparently rapid and by Noveeiber moot of the sections show the testis to contain a considerable nunber of sperms, arranged in the characteristic eolusmay nsuaner (Pl*3&, fig*1)* By this time, the follicle cells have disappeared from the centre of the luaina vhidi are now filled with sperms (Pl*38, fig*3)* A few spermatogonia and spermato­ cytes arc present in the peripheral region of the f dH oles, but the bulk ef the cells are spermaiosoQ* There is little change until April, when proliferation begins again, and by the middle of May, the lamina are full of cells, the central ones being eperas, and from there to the germinal epithelium there exists a progression of spermatids, spermatocytes and spermatogonia of both orders (?1«38, fig* 3). There is now no definite pattern except in the arrangement noted above* During June males are still/ 1*0# / s t i l l rip e n in g , although some may have spawned in l e t s Hey# As with the ova, the fat© of the retained sperms is doubtful, hut the occurrence of many of these at a l l times of the year, in addition to the fact that only a small percentage of the males spawn out completely, suggests that they, too, are discharged normally during the next spawning season* Follicle cells are not as apparent in the males as they are in the females* This may he because they are not as easily observed owing to the presence of residual sperms in ouch a high proportion of spawned animals* However, in the animals which are eoGg>letely spawned out leaving the centres of the lumlna wqpty, the alveoli become filled with follicle cells as in the ovary (?l#39t flg#0* Spermatogenesis appears to be normal, the details of which need not be repeated* The male breeding season then, consists of a period of recuperation during which there is proliferation of follicle cells* Zn conjunction with*this, there is a certain amount of semnat ogenesls bet worn Septesbcr and Havener, idea lower temperatures apparently curbs activity* The m issis go throu#i the winter with the testis containing roughly s quarter of the possible sper® content* Spermato­ genesis Is renewed with the advent of hitter temperatures in April, and by the middle of June most gonads are extsnaed with ripe gametes*

jjggJUUA* Of the 925 animals sectioned* 103 were fconic*' sa*». /feaslfti rad 467 were males! the sex of the rraiA hg f9 » was not determined* Thus the eex ratio ia approximately equal* Only one hermaphrodite wee found (F1*36, flg*f), comprising 0*f£ of the population sampled, indicating that the species is normally unisexual* Approximately 1# of the population was parasitised by a treroatode of an unidentified species*

Discussion. A study of the seasonal gonad changes in pul^astra shows that after spawning there is a period of recuperation followed by a short period of garnetogenesis* Development during most of the winter is at a standstill or proceeds very slowly* The advent cxP higher temperature in early spring initiates, or accelerates, production of gametes, and most animals are fully ripe by Hay or June* Spawning occur© between the middle of Hay and the middle of September* spawning may not be completed at one \ operation, but it appears doubtful if a second crop of gametes are formed and released during the one spawning season* Completely spent animals, especially males, are seldom found, as residual ova and sperms in varying quantities are usually present* This cycle is similar to that found by Loosaaoff (1937) for T.eaus mereenarla of the Atlantic coast of America, althou^i the gonad type of X* ttuiiaatra resenbles that of Msm arm aria (Coe and Turner, 1938) awe than it does X* m t t m r t t * structure of the gom>d and the seasonal gonad changes,/ t s s . /ota& am t oX oraly reaeufcle that of the Pacific Coast Z a d ti* gft»«HW» U w rft* . m 3 ) . Zn m m n with X* “IfFffTMTtf - Pert ®f the gonad development takes place, as pointed out by Loosanoff (1957) during period* of rather low temperature** In other apeeiee, notably the oyster*, the time of gamete production ie confined to periods of higher water tempera­ ture*, as in late airing and sunaer* Ho gamete formation takes place in Ostrea HRMPMIW olgaa w ill the following spring* —— —— Amsmtya (1929) and Coe (1932) found th a t in £ • lu r iq a also, the main, period of garnetogenesls after the last summer spawning, i s i n th e follo w in g sp rin g when w ater temperatures begin to rise, and the sane is true for £• fyjywMi^li* (Houghley, 1935)* However, in Ji pm iaatra. too, the increase of temperature in spring brings on the final ripening of the gametes* Unfortunately, the sampling did not go bade into the early spring of 1948, so the condition of the gonads then cannot be compared with their condition at the same time in the spring of 1947, Sen the water temperatures lagged a fu ll month b However, the effect was operative in that epgntwg in 1947 occurred a month later than it did in 1946, and no doi&t, part of this may be attributed to retarded gonad development a* wall as to the late incidence of the so-called "critical* spawning temperature* On the question of the fate of residual gametes, Loossnoff (1957) agrees with Orton (1953)# that they are/ 1 2 6 , /are finally discharged before the winter* It la certain that this la net the esse with J# m^laatrs and it is tentatively suggested that they may be retained and spawned In the next season* Ussy (1953) states that the sexual produets of £« glass nay be serried tots or throughout the winter and nature eggs hare been found to April* normally the unspanned sexual produets are resorted during the f a i l and early winter*

5. £ . C.i-' *' . f ; ij* . ' ^

4. " ' * '

i$.¥-.. sv» . ** -•%, ‘ j ; i ■ r4*‘ 12?* Crawth* A large part of the information on growth In lamsXltbr&nohs ether than oysters, ie based on observations «f Horth American species such as* Tivalla ataltomai (w©ys»uth 1923); S lllq u a u a tu ls (M oSllllin 1923; Weymouth* W llU n end Holmes 1925) I Yanas mercenurls (Kellog 1900) I Boslnls discus (Crosier 1914); jtytllae eduila (tlossop 1921* 1922) nod Hye a re n s rla (Heweofifi* 1935s*hte ; 1956s *b)« Tor British species there are the observations of Orton (1926) on Cardium edulei Stephen (1928* 1929* 1931* 1932) on Tellina tm nia and several other epecles; Ford (1925) on a masher of sUblittorel species; and Davis (1923) on S o isa la stifttruncata and Hectrs stultorum from the Dogger Bank. There Is need for further growth studies on lsmsXllbranehs* especially of a comparative nature* Growth in Xasnollibrancha m y be studied by any one of* or e combination of* three main methods* 1* Keesureawnts of individuals from random samples of a population* 2* aueees&e raeeeurfraonte of marked indi­ viduals* 3* Keasurement of enxracl growth rings* if their validity as indications of seasonal growth has been established* Adequate data can be Obtained from randan sang&ee only when the breeding season is short* so that each new brood enters toe population as a well defined group with a limited else range. If the speoles has this eharasteristic* each year class will appear as an isolated or nearly Isolated mode in a else frequency/ /frogmeney distribution* This is well illustrated by Wtaekwcrth (1931) was able to separate two wall defined groups in gmdiis unduleta* and determine their age and rate of growth* If, however* the breeding season id extended* there will be a large range in also* and the large animal© of one year else® may be confused with the smaller animals of the succeeding year class. This* combined with individual differences in rate of growth and differential mortalities* lim its the useful­ ness of this method. The successive measurements of narked individuals Is the most direct method of measuring growth* and marking lamellibraaehs ie not difficult* One disadvantage la that eech tiraq the animals ere removed from their habitat* growth stops end a disturbance ring is forced* Orton (1926) discusses the formation of disturbance rings in Qardlnm e d a le , a s does Weymouth {1923) f o r T lw alia etn^taamnu and as there is no essential difference in ]£• m llaatrs further discussion is unnecessary* The amount of growth lost by disturbances may be calculated and adjustments made, but frequent disturbances may have a significant effect* The measurement of annual growth rings provides an accurate method of estimating rates of growth* In this case the animal is unmolested, other than by natural disturbances* The method hinges on whether the rings which appear as surface sculpture on the shells of most/ /most lemsXlihrsachs am annual or seasonal in nature* Weymouth (1923) lias reviewed the literature an annual rings of mollusc® and ho sum up in thane words: "Of fourteen paper* by thirteen different authors* on© flatly denies that age can he told from the shell* two are unwilling to conrnit themselves* five feel that there is some sort of connection between age and the lines* hut that they are of no practical use even if their annual occurrence could be established* and six go on record as believing that the rings are annual, though only one of these actually makes use of the method in constructing a growth curve. In only two can the oaee be considered as firsflLy established on adequate data*" Weymouth himself goes on to establish beyond doubt that the ring© in Tivella atnltoram are amuol and can be used a© a means of measuring age and rate of growth* He consider© in detail how the shell is laid down and how the rings are formed* Since then a nuisber of anthers have proved the validity of the rings as measures of annual growth for a aunber of species* Among these are M Cillln (1923)* Orton (1923)* Ford (1925)* Fraser end Smith (1923) and IfewcoEtoe (1936)* It has been shown* however* th a t in c e rta in specie© such a s ftoainia / dlacu* (Crosier 1*1U)» the annual ring nethod la not applicable, and Its validity most be prove* for every epeelee. Wit* £. nniiaetra- ell three o f the above mentioned Method* have been need, one serving aa a ciuscV m * /chock against the other, A large Busier of animals vers sexed as the shall* wars opened prior to fixation of the gonad for the work on seasonal gonad change* hut no striking differences between the elses of males and females was Observed, Such difference* would have boon e m mere apparent when Observing spawning animals* Fraser and Smith (1928) investigated this point with Panhia sfrsataBa and gisantens hut found no dlfferenes between the sisea of the males and females of siodlar ages* nor did Weymouth, fSeBtllia and Slih (1931) with the saser dam Bilious natula, though they refer to Gbnbadfiia (192?) ae having established that* "Zn seas nolltteee there is sufficient sexual dlraarphicm to permit toe recognition of the m xfef m individual by toe toell*" It is possible there may be a difference in the growth rate of the sexes of Jf, pullastra. but it would be detested only by careful statist leal study* a»d for toe present work the equal sex ratio glvee equal weight to any possible differences and no distortion should ensue* Zn thlo study* length is the measure of growth that will be used moot extensively* for thle factor appears to be as good or better than any other such as weight* height or thickness* Height (dorse-ventral measurement)

Growth in the. Young* The normal breeding season of 2* mtnmrnmp 1

fflh 111 fifcjftotal m m w m jtik flUMftlMft Mi„SM&wl&.MmSL&t tofiUL

Ring Sample Range Kean Variance S tandard Standard e ls e D eviation R rro r

IT! __ 1*10 - 5*09 3*91 0*92k J ) ^ M > r o t 64. Lftmrth lliS 1.10 - 6.89 i M - « & & £ _ f

ffffn? ?rd« 19k7»

KiBg S e ttle Range l e a Varlance S ta n d a rd S ta n d a rd s i r e D e v ia tio n E r r o r

201 0*70 - > M P *2lp o .o n P o t« l EtllldSIl ,. i a t ..... lel2.--.7jA ifctSl.- J l . .

i / o t 1*0 anu The increment between the first end the second rings in large samples of adult e from the Cross House 8 Beach in HilXpert, is 7*7 mm. , with a on an m onthly increment of 1*3 mm* for a growing season of six {souths* Bore information would have been desirable from further samplee of animals in their second sumraar# but the mean monthly increments derived in the two ways indloated above* are olose enough to provide a reasonable cheek* Xn Table 15 are given the length-increment frequences for the various length groups of spat (length of ring 1) and it" is iogtortant to note that over this particular else range, the larger increments are gained by the larger animals* Xn comparison, Table 18i shows that for the adult sise groups the converse is truef the larger increcents are gained by the smaller animals* Whether this is true for other species is not known, for this early period of growth has been little studied in t h i s way* Xn T able 16 are given the absolute increments in length for the various slse groups of spat* and the percentage increase in length, which also increases directly* For complete analysis more data is needed on animals ranging from 0*6 to 2*0 cm* In the marking experi­ ments, discussed later# the highest mortality occurred among the smaller animals, and only a single animal with less than three rings survived* TABLE 1 5 .

m j m i a m .flat* Ufflftft l§ m , f . a « t t i S pj$gy jpfii,.iDfm|«air.MftliMrtllll .tm ,tag la froia the start of growth in Any 11 to Jana 3rd.

w f ► Point NBMlfc...... _...... Winter fiiM 0*25 0 .7 5 1.25 1.75 2.50 ► k ...... 6 > 2*08 .. 13...... 5 — * 1 ir^2*87 ...... 1..... 11 ...... 3_._. ► ■.. ,.J5p86 ...... I...... ,...3 ..... 27 k ► 1 ...13 ... ► 5.2k r.__i.. ... lit 16 0 ...a ~ f ■ i f| 3 . . i t f t L . , —L- -JL- 6 11 ;l tugtk-lncrenwot TaMl«. I m t w w at Varlopa Langthaof S3B*-fr«a tha Formation of the Wlatw Ring to Jim* 3gd.19U?.

Length at Ouwjla tfean # Increase Winter King 81»« Increm ent In Length*

•9 .• 1*69 ...... 1 0 ...... 5 5 ______t e .o ... 1B____

15. 1*31 - k 5 .o

3*3 k*£8 . 35____ 1.76 36 2*19 _ 1*8.0

. J i .90... * 5«i59 ..... 35-.-. ______51.0 5 . 7 0 - 6 . 8 9 23 3.16 52.0

------M .0 1 3 5 .

Xoalhli samples* A eerie® of monthly random samples varying la else fro® 100 to 200 animals* were taken from a limited area on the Gross Houses Beech* This beach has been described in another section and as'far as could be ascertained* carried a larger population of 2* tmllastrc than any other on the island* Even then it required at least an hour to collect a ©ample of 100 animal** The sampling technique consisted im vely of turning over the flat rocks« taking the specimens showing above the surface of the sand* and then digging over the area with a small trowel* A more efficient method of sampling would have been desirable* because of the difficulty in finding the well camouflaged smaller specimens the mangle* are somewhat biased toward the larger else groups* Owing to the rocky nature of the habitat* and the comparatively small amount of loose sand* sieving was impossible* The information from this ©cries of ©ample© le ©umrnarlsed in Table© 1?A, B and C* A ty p ic a l le n g th - frequency distribution is shown in Pl*h2* where the dominance of the larger animals may be noted* a© well a© the absence of a definite eerie© of mode© indicating the various size and age groups* This la no doubt a reflection of the considerable range in length of each year eXass resulting from the comparatively long breeding season and the overlapping of sizes in the older year das see*/ iiejtgtk - Frequency Distributions of Venerupis from Cross Houses Beac&i 1

Mid 19U6 JEM P o in t May June J u ly Aug Sept Oot Hop Bee FeM Mar Aprl T o ta l

i* 2 5 — f 2*22 m a s . 1-4 2S. 12*25 JL 2 , -21 lk 2 4 1 2 . k . 11 11 .k i.2 i l 1A ..25 6 12 . 17 .88 11 .31 1 2 1 1 M 5 11 12. 20 - 2. A 122.

20.25 22 I 10 12. 12 . 8 8 22 22.95 2L. 12. 15. «> ■gk24 O 20 II 21 12 11 A 12?. 26.95 12 22 21 l k 12 12k JMhrg 31 JS A 12 12 11 2 l-J- 1 2 k 12*22 Ik . 12, i l A ± L _ 2 2 12 2 12k 32.95 1 1 11 11 23 40 4 2 JL lk? 2k *25 11 kS. 12 1 2 XL l k l i l k 18 ? 1-8.25 11 29 8 1 2 12 22 8 40 3 2 1 1&25 2U 40 1 2 12 12 11 1 1 2 16 8 41 A J2 _ ^2.95! 1 X M. mSBSSltk-'m X X 1 2 . M >2! ± fafl.9' 1 TABLE 17 B. j LEjGTH - FREQUENCY Table of mid-monthly samples of j Veaeriipia to show lerarthfrecmencleB a-j various acss j (ring numbers). Length in nw. !

j,

a i a . p t . ! • I t 2f 5 t ^ t- r 6 . 7 t 8 , 9* . _ 6 ,9 5 2 __ 8-9 5 k » 1 0 .9 5 SI k_ - 1 2 .9 5 SI to * n 36 3 6 1 6 .9 5 „ 1£ ... 2 9jl 1 1 8 .95 $7 9 - 2 0 .9 5 . 7? 16 2 f 36 HP H 1 2U.9S 36. 75 4., 10 1 . 2 6 .95 17 86 19 ? 2 8 .9 5 £ ,6 0 59 % 1 .10*95 62 20 >f ’ * i 32*95 21 7* ,.H1 k 30 3km 95_ - 9 58 9H 1 ' I, 1 6 .9 5 1 29 7H HP 7 it 5 8 .9 5 7 H5 H5 11 a 1 6 0 .9 5 17 57 Iff j 4 2 .9 5 6 18 1 5 , . 5 J y u 9 5 .... 1 „ ? 9 5 1 1 6 6 .9 5 .... 3 ? ..U i 6 6 .9 5 1 4 * T o ta l I 0! - 2 2 1 362 JH2 3 0 ^ 1 7 1 22 I TABLE 17 C .

| i

S tatistic* QfJMa.Moat.iiiT ffunmies gfTonewipla from the Cross Homes Beach. The Measurement is to ta l length In bml

Date 3arapl© Range lean Variance Standard Standard siz e D eviation e rro r

K a jtM 121 6*0 «a»45*9 28.27 1.837 8.586 0.780 JtattehS 120 9*0 mm 45*9 28.1*1 2.027 8.988 0.822 JnneU6 f i t 8 .0 45*9 51*39 1.742 7.980 0.732 J o I t 1*6 101 8,0 45*9 ?9t76 1.496 7.680 0.768 ... Aug. 46. 103 _ 1*9.9 24.11 10.056 0.966 8ept.i*6 tSfO mm 1*5.9 29.01 1.55SL 7.878 0.600 112 10,0 -I. 35*9 2?»i?5 1.053 6.452 0 .6 1 2 _ O et^ k& 157 10,0 47*3 50, 6? 1 ,7 1 3 ... 8.088 0.648 O et. yf, 119 10,$ 45.9 28.76 1.550 7.860 0.7 ^4 Get. IsS 179 «»47*3 28.90 1.784 8.320 0 .624 Worv* hB 128 fo*0 4 9 .? 27.89 1.989 8.802 ilfi 15h 10,0 43*9 29*07 1.803 8.202 0.664 _ P et* h ? 95 16*0 «* 47*? 31*66 2.242 ...2*M 2. .... 0.974 MS 8.083 0.706 Mar. h7 132 1o ,o 4?*? ff7*3& .-1.S&L.. ■ A m 47 ..8 2 — 1 ,-0 - 41*3 28,81 1.762 8.278 0.836 Orton (t»$6) describes the growth of young Cardlua sduls as overtaking that of older animals* Weymouth, MeMillin and Holmes (1925) found difficulty in Identify log ego 0 W * to their length^frequeacar distribution* of glllona

A striking feature of this series of samples Is

the extreme variability, as may he seen hr comparing 1a Table 17C the means of samples taken in consecutive smiths, as sell as in different samples taken on the same day (those for October)* The adequacy of the samples could not hare been Improved without difficulty* Bach time a sample was taken a new section of ground was used* so the fact that samples were not returned, should not haws influenced further sampling* The whole beach is a eosg>arativtly small one and a ll the £« psllastra ground le within the tidal range of one foot or less, so that the growth rates from one part to another should not wavy significantly* In addition, there Is no real evidence of the presence of dominant year classes* Therefore, other than providing animals for the measurement of growth rings, a series of random samples Is of little use in determining the rate of growth In 2* pullastra la thin a re a .

The mala object of the narking experiments was to provide a cheek on the information derived from the measurement of individual winter rings, and to test the/ 1 3 7 * /the validity of the rings as measures of annual growth* The animals were marked ta several ways; the a»«t satisfactory one was to susber them with India Ink m d oovoi* th i s w ith a la y e r o f d istrezie d isso lv ed l a Xylol* This method gave the clearest mark, was easily applied end caused little disturbance to the animal* Its use la limited to animals having comparatively smooth shells. harking nunhers on the Shells by mans of a dentist's drill was also used, end notching the shell edges with a file gave a permanent reference mark* After being marked* measured end the age estimated by the annual ring method, the specimens were replanted in half inch me ah galvanised wire eages* These were burled in the beach tint 11 the flat top was flush with the surface of the eand* after which they were filled with sand and gravel* The animals were planted Jest below the surface of the sand and the top of the eagc Closed up* The eages were deep enough to allow burrowing to the maximum depth of which this species is capable* The beachm which the cages were planted was a gently sloping one composed of sand and gravel, and carried a m il population of £ . pullastra* It was located on the northern side of the Island and chosen because of its comparative isolation and the suitability of the substratum for this type of experiment* The main experimental group of animals were planted on Septeaber 17th, 191*6 and firs t examined «✓ 13a* /on April 26th, 1$»?« The m ortality over this period wa® about 2*$* Only a few young animals showed a fin e silver of new growth on the ventral shell margin, and measurement indicated no change in length* This showed clearly the winter ©sanation of growth as far as th e external dito&mjlone of the shell are concerned, and th a t new growth was Just beglnaic^# The temperature at this tim e was 6*0® 0* as measured at the surface at Keppel Pier* The m&m l& vere next examined on July 16th and finally taken up oUt October 15^7# uioita 1 ity^ had increased by this time to 6O5C and was centred, as mentioned in another section, on the younger animals* Sow growth had occurred in practically all and was easily distinguished by the shite new shell. In contrast to the dsn colour of the old* At the margin of the shell where the new growth began, a groove had been formed, separating the new growth frees the old* In addition, the file mash on what was formerly the edge of the ehell coincided w ith the position of the groove* The £ieen increments fo r the summer p erio d of growth are shown In Table IS and graphed on P la te k5* These date are taken from 109 animals, the s&yvivor® of a total vf 2fS originally marked, and gave an annual mortality of 62$* The high w rtality is a decided weakness in this type of exportont, especially ^hen the mortality in selective, In Table t

m SyBBSflbi

Ut&Q Sample Rsnge l o w Verlanos Standard Standard siz e DeTlatlcm OPfOF( 1 T r , r r n ffrJLr._ ...... -J 2 €*60

1 .. Sb. „ jM f , 1.39* 1.857

.....it . . 30 U.55 1.050 25 O i l - €*5.. 2.1£

6 ... 411 -JUM Q.A62 ^ ! ¥ 6 ~ .... - y - ...... >’

...... k - 1 |* ‘ n W ------T ' ^

Jl TABLE 18 A.

TM m LM jm ssL 3 3

...... R i n a R u < * « ...... -— ...... l o c r e r a n t . J*_...... 5 .... . J f a f c..... 5 6 r 1 * 1 * 0 ^ 5 . . .1 . . . . ^ , 4

4 k 4 2 4 „ 2 JL- •

• 2 * 0 ...... 0 I 2 ..... 1 ...... 3 . . . . 4 ___ 2 ...2 * 0 . 3 * 0 ... . ,..... 2 ... . k -. . 4 .. 3 * 4 ~ 3 * 5 _ ... 1 , k 4 . .1 . i 3 * 6 * * l i .*0 k ..... 4 _ 4 .

L i t — ^ .* 5 ...... * .... - _ , k . 2 4 U j 6 - 5 .0 ...... 8 ... . 1 3 *4 * • 5 * 3 .... .2 P f e _ 4 5 * 6 — 6 * 0 ...... 3 ...... 3 . . . r _ J L _ 2 . 4

. « * 7 * 0 ... T f T 3 ... . 1 ..... 7 .1 - 7 .5 ...... 1

7 * 6 ■ * * 8 * 0 ...... 1 8 .1 - 8 .5 2 i 6 * 6 • 0 * 0 2 - I • i 0 * 4 - 9 * 5 ... St— i 1 LmJLmm 439* /wide rang* oaf lengths* Ring 1 is, unfortunately, not included,for animals of this else ere difficult to mark satisfactorily, and ©ran then there arisen the problem of keeping them in a natural envlronrrent* It wee hoped to gain thin information indirectly by the measurement of spat, hut the mortality wee no great, an deaerlhed in another section, that a represent at ire sample could not he obtained after June, 19b7* However, much of the reouired information hen been obtained from the measure­ ment of the appropriate rings in adult a, an will he desorlhed in the next section.

MecBurement at Am from AtmoaX Growth R ing.. Based on the above conclusions that the ring markings (Pl*hb)»or At least non* of them, represent annual growth rings, or more accurately, winter cheeks; these were assessed and measured* After some experience and basing judgement on the nature of the various rings and their position relative to one another, reasonable estimations were made in the majority of eases as to which were true cheeks* Many animals showing numerous or ill-defined checks were discarded; others were measured, but when inspection showed they did not conform to the sigmoid curve of growth, they were put aside* A limber of animals were not used because the ring markings were worn away by abrasion* A typical example and one of d is to rtio n , ore shown in ?1*1|5* Whether th e ab rasio n s a r e / /are the result of movementb of the animal against the rock on which it wee lying; or o f the movement of the rock against the animal, is not knowxn possibly it is a eoufeination of both* From a series of 12 random sables from ths Cross Houses Beach, about 8*000 ring measurements were made, of which63OO were used in the compilation of length-frequenoy distributions from the individual rings* During the growing season the measurements of new growth were segregated from the other measurements, so that only rings formed during ths fhibernation* period were used* All the measurements of each ring number were grouped together to obtain a mean length for that ring* This compilation is fhown for each sanqple in Appendix 2* The information was further condensed by averaging and the final result is given in Table 19 and this forms the basis for the growth curve in P1*J#« In addition to ths arithmetic means, the median values were calculated and they are also listed In Table 19 for comparison* It w ill be noted that with each ring the two measures of central tendency are nearly identical and indicates that the distributions conform very closely to ths normal curve* Examination of the tables shows the large variation in the lengths of any given ring, but this is to be expected, for in these measurements are included not only lengths of cooperative rings of animals of ths/ X sU i-1 2 *

JBafiSI I f l3HSSJJjK B -ill ijrw" i m^mmmrn Cm

EfclDgj Ho* of la - ^ lnOTOBIBlXt. Ho* 880(308 [loon UWf-* saral InowMiil Qoqgai of iw ilou ring)

_ t 12.... 3.65 3*39 3 .6 5 8 12__ 11*3*1 7**7 ____200 1 12 Ifa ff I f *21 8.5B ti 12 « . 7 . M.1 2LS0 8 * » ...... W) ...... * 12 53JHLTftfO - ... - - » .....- - ..... —1 f 12 3 7 .3 5 n j a 3* Si ...... 10 ...... T 12 . -...... o ...... - . . 1h1* / t h e m m year class but also those of a nanbar of year claaees* For example, ring 8 of the t938 year elase was formed In the winter of 19i$*4|£, while ring 8 of the 1939 year class was farmed In the winter of 19h6-47« Thus the final mean length of any ring is derived from the growth rates of animals of like ages In a number of different years* Growth rates are known to wary from year to year (Orton, 1926) depending on temperature, food supply j and possibly to factors not yet understood* Coe and Fox (19Ml) found that the average monthly growth Increment in the California sea mussel (Bfytilua califomianug) showed an annual variation of more than 98 fg* Thus the growth rate of X* PuHaetr* determined In the above manner, possibly gives a better general m m value than the information derived from one or more years by marking experiments* There is the lim itation that the higher ring nunfcers ere not so well represented as the smaller ones because of the normal increase of mortality with age* I n Table 20 are dhown the anonal growth Increments between the formation of the various rings derived in several ways*- A* The mean length of rings from a large pompi* o f anim als (6300 measurements) of various ages from the Cross Houses Beach* B« The mean amount o f npw growth during ths 19b7 growing season at the Cross Houma Beach, calculated partly by emanation of monthly growth/ gagman aonof mount (annaal) of growth b

A* Average lengths of rings from large sample (6300 measurements) of animals of various ages from Cross Houses Beach* B# Average amount of new growth during the 191*7 growth season from Cross Houses samples (UU3 anim als;* C# Average amount of growth during the 191*7 growth season from marked animals on a Beach - ths north side of Croat Conferee {109 animals)*

Annual increment, in mm.

Between A B C

0 - 1 3.65 1 - 2 7 ,6 7 ______% ..1. — 8*58 2*^8- 6.60 1 H -l

* - « ~ ------J*M tk%* /growth increments (Teble 21), and partly By th e measurement of the total rasaer's growth (Table 21 , 20*10*1*7) from hi»5 animals* 0* Ih e mean amount o f growth during th e 19B7 growing season obtained from 109 marked Individuals (Table Id) grown on the north side of the Island* Increments in A and B are auitc close and indicate that from the point of view of growth* 19*4? approached what might be considered the norm of recent years, in spite of the delayed rise la temperature after the sever winter and early spring* In 0* the increments are lower and this may be accounted for by the fact that they were replants in a not entirely typieal environment* But in the main# the increments as derived in the three ways, tally closely and indicate in another manner that the annual ring method is valid for estimating the rate of growth in £♦ uailftstra* In addition, a total of 1300 ring measurements from the Cross Bouses Beach samples of October 15th and 16th* 19M> were plotted to show the length frequency distribution (Pl#i*7) • Theoretically this distribution should give a multi-modal curve, with the nodes represent­ ing the lengths of the various rings* However, only the first two modes are definitely significant of the first and the second ring* The modes thereafter are not distinct enough, that la, there is little difference in frequency between the minimum values occurring between two/ TABLE 81.

hSmWUIIMWb

A pi ~ Kay - J’tme - JtO jr- Allg - f a t a l Kuan Blag Kay J v m J u ly Aug 8dpt Xaare- Znera** ment

____ 1 ...... 1 4 9 r i.« o _ , 1.3 0 0*93 1-06 7.8* s ...... O+lift 2.33 J k i l „ 1.38 9.71 1 .9 k ^ k _ .... 9.79 3.11 0.38 0 .M IT-~...S...... ^*08... .. - 1*30 .. 1 .M 5.00 1*25 6 I s l t i 0 .6 0 0 .7 2 2 .3 k 0.78 n i t 1 4 5 , 0.1* 0.38 2.20 0.73 ? T ptal da€e T o ta i Increm ent 3«50 $#**6 <0*27 1 2 .3 3 5.6U t m A ll aaas . ... 1 ~"TK aa 0*8? M 3 1 4 * 1*7* 0*80 f a r A ll *d flffflf

J TABLE 21 A.

ggffiw iff g t ,ft«g " m m m a f i i, jd u e a i f m ***■ f » a Cf*** Heme* eampl.ee I

D ate Ming Sample Sang* i m e lm

1 ___

— ..3 ...... « — 0*2 * 1*3 ...... O.JiS k ...... ___ 17 .. .., ,0.75-...... 5 ^ k ..... ,. 0.^ -1 .0 0 .9 2 .6...... 2 ...- . .... 0 .6 0 _ 7

1 8 -6 ^ 7 —.. 4...... :.... i 3.1tf i i

.. 3 ___ ...a s...... 0.5 - iufc auai .. ^ ...... - .... 36 ... 0*6 - 6 .6 5 ... 2 5 ____ ..... 0 .9 2 ..,... 6 ...... _ ... . 1 2 . . - 1.01 7______...... 2_.. . 0 . » ....

17-7-k? , .... 1 _ ..__ 7 ...... , 2 ...... 3 ..._. 5 .3 ~ 6 .0 , 3 ____ ... 37...... b .1 9

.. hm&..... 5 ...... 17___ 2-00 , 6..._ .....6 ..._. .... 1*0# 7 .._ 1.1 * let 1.WS TABLE 21 A .

Bate S lag Sasg&ft Sena a lse

21-0-4? . 1 ..... -T-r,.-Ti^ ... . 7»3 * tliil 6*93-

- 2 r 5 _____ ... . J* 0 • iO il ...... W ......

1 ...... » ...... _ 8 .3 2 _

T - 4 ______...... - 1 2 ...... _—3a9. «■*... 9*5 ,r_...... 5 ...... 13____ to* * 5eli 6 6

~ ? .- .... _____ 6 - ■ ^JttSL sA I------

21-9-47 ...... 1-...... - ...... - ...... 0 ......

m.....St ...... JT_ 25... . .

, - — 3 ...... 2 9 ...... - 9-7*

^ h .. « ____

nT 5 __ __ 8 . - .. . 6L ~~__ 10 -....1^3. - -6 » k...... 3.29 , .. - 7 .. .

n -,,8 ------...... 5 ------l— ------20-40-4? ri ..... 1 ______31 5 „ 33 ....

4 ____ ...... « ..... 9 * 1 -

§ _____ ...... IS...... J i.3 *

, *_ ... 1k # p 7 ...... 6 ... - oi os 9.93 %L 9 4 .9 « 4 .7 145» /**© pe«** and tbe peeks themselves, This obscuring la ♦ 110 doubt due to the overlapping elsee in the older /tar alettes* However, the first sod second rings are definite enough, and the modal lengths tor respond well with the mean v alu es in Table 19* Boring the growing season the new growth on the animals of various ages was noted In the monthly random samples and this information has already been utilised (Table 20) ♦ It is also arranged separately in Table 21 frost which the mean monthly inurement, is obtained, end this is plotted on the graph, Fl*l*8f along with the mean weekly temperature for the period* The growth increment curve fellows the temperature curve very closely until the time of the first spawning (sp«) when the increment curve drops* This would be more pronounced if the m ature animals had not been included* A similar condition exists in the Please dam (Coe 19h7) where there is an Increase in the rate of growth with the spring increase in temperature up to an optimum when growth fella off to a mini mom in August, although the water temperatures are then highest# Coe considers the decline in the growth rate ae due to »the requirements of the reproductive system and the successes acts of spewing** The seam trend in growth takes place in both species of Mvt 11ns found in California and in other invertebrates there (Coe and Fox 19M*)« They consider that food supply has more influence on rates/ /votes «f growth then have small increases in tea$ievsture«

on (1998) has 9 m there is a spring end an autumn period of shell growth in Qatea edulis with little or nans during the breeding period when the temperatures are highest# fie concludes that shell growth Is a function of temperature and feeding and suggests a physiologleal antagonism between shall growth and breeding# With ]g> m l last rs « at least in 191*7» th e su an er decline in growth rate coincided closely with the onset of spawning and the decrease persists for some Hue# According to Marshall and Grr (1927) there is the usual spring increase in diatoms in the Millport region, but the autumn increase does not appear until growth has almost ceased, although ths temperatures at this time are still high* It would seem that there must be s source of food in addition to diatoms to permit growth during the period when, the diatom population is low* A sm all m la^m sm er bloom o f diatoms is normal and in 19h7 it appeared to be greater than usual* The Millport plankton is rich in larval forms and other small organisms throughout most of the stumer* Coe and Fox (i9Mt) consider Ms bulk of the food of ftrtllua aallfomlanua to be detritus* Coe (l9h7) believes that the eggs and sperms of algae and invertebrates fora the food of the Pisao clam as well as detritus and living phyteplanktcn and sooplanktosw Mo ettcapt was made to investigate the food of mniiaefera. for there is as reason to doubt that/ 1U5* /that it is unlike say other suspension feeding laaelll- branch* A correlation between the amount of food available throughout the growing season and the rats of growth in various animals would be of Interest*

l a T able 22 Is shown th e h eig h-len t g th r e la t io n ­ a l pa for spat between the lengths of 0*5 and 5*0 mm. 9 and in Table 23 la given the h:?lght-length and the thickness- length ratios for animals between 10*0 and 1*5*0 mm, la the early part of the range in the spat, height tends to approximate to length, but very soon, at a length of 2*0 mm* ths ratio changes to that found in the adult* The helght-length ratio in the setting larva Is 0*92, and there is a grateal change from a nearly spheriaal shape in the larva to an oval shape in the older spat* Ths oval shape adopted quickly by the spat has its advantages for burrowing* Xt will be observed from ths tables how relatively constant the height-length ratio is maintained in comparison to the more variable thickness- length ratio* This variability may well be a reflection of the variable consistency of ths substratum* If this la hard and unyielding, It may prevent the shell from assuming its normal shape* Certainly some of ths burrows have had walls of nearly rock-like consistency. Ths thlckaese-length ratios for Tivella stalteram (Weymouth 1923), a pure sand dwelling form, appear to be mors consistent than those of X* uullaetaes* These ratios for/ TABLE 32

gffAiM. 9TfL fe w i o m mSMm‘ a m m m M m w a rifcrn JBtStjSSJ^flsfeS Cfciaafi# JhS^BSSSi&£SS£qLm«nBlJBK*

ft£& B a m p la L e n g t h P o i n l m t m z » a n g m

0 * 5 * 1 ______M ...... 0 . 5 7 8 0 . 5 2 3 . ... . 0 * 9 0 6 ...

____ -1 -6 1 ...... 0 . 9 0 1 r . 0 . 7 9 7

1 . 2 6 1 ___ 1 * 0 ...... 0 * 9 ir t ..... _ V * /P Ji __

_ i . € M ...... - ...... 7 5 ...... J. 6 3 p_ . ^ 1 . 1 6 2 . .

f a ® * * ...... 5 6 ...... 1 . 3 U1 _____ , Ir. 0 . 6 7 0

, 3 1 ,...& 5 9 0 ...... 0 . 6 § S

2 . 7 9 1 , 2 3 ...... i .t m _

1 .1 3 6 1 2 ___ €L&ti9

% CCK4 1 1 -

5 . 9 0 6 ____ 1 0 L _ a . 3 0 © _ 0 .6 1 4 7

...... 7 _ , , ..JM»- ...... a . m 0 «6 k 7

...... 3 _____ . U. 6 6 7

...... & - 5 . 0 6 2 _ 0 . 6 7 0

6 TABLE 2 3 .

fflEm BMsai m k s m a J II^ ^ MftfiJPtf ttfftf [jtiKLJULJP*

no. or H elflht Specirxm Length H eight T h ickn ess Length

i S l t i US. £ L jJkSSLi j S. JEtA J&&. Hi i M !&•! 11 S i f t 12M1 JZtdtt. JIIS il 1§2*M MUZ. M t& L j U k , jsaSkS. m s s titl.SS 2 £ * lk ikSL JSSS mSl 11 >28&c3& lfibO L t2>5 M jiSStstiflL iS S d S i m u i £ l (ft A JSL josmM. 179.89 125.38 juBSi £ 11 ISfeuQE. m$sL ML m s 1 1 sNEKKIUUkS0C.7S m m 1M*JBL j S. JM m sawa JflSeSl ik SMBBOHMlh23h*li2 jkS*29L S d .asgaJaaics 17S»00 jkft ■3SSU5. i l i26s28L j £ £ L M 8 i l JL HS*9fc Jg fJg . i£BL -*Ji2SL__; MUL 1 £Ql ■tSU UMI.l us

I i k f i . 2* JB&leaiga ere plotted In Pl.l*9 and the graphs represent the average relationship vhioh Is staple and direst with no radleal change in shape with age* Crosier (1914) in his study of Doelnia dlscars also found a simple tangential relationship!* The ratios for the sise groups above 2*0*0 n mu in Table 23 Indicates that growth in length may he slowing down slightly in relation to growth In height* This point has been Observed directly in older animals whore no new shell growth Is evident on the ends of the shells* although there may be a small amount of new growth on the ventral edge* It may also be noted that new growth in young anlmtls first occurs on the ventral margin of the shell*

Plaptt ssion* The mean monthly growth r a te o f J# tmi has already been ©©Beared with that of other lam slll- branchs* Direct comparison of growth is difficult when dealing with different species from several localities* from examination of the modes of his length-freQueney curves for ^sHlna tenuis. Stephen (1929) fd h l that the «nr*u*1 increment of any one year class decreases at a rate of annually, whleh la in agreement with the data gftgdium edule (Orton 1926)* Stephen points out that if this rule holds good for all lamelllbranchs, a means Is at hand for estimating the age of numerous small but economical species, when only the first full year*s increment is known. But, as pointed out by Blegvad (1930)/ ih% /B lared (1930) the matter is not quite eo simple, for the growth rates of sveral Deni eh species do not conform to this rule, nor does the growth rate of 2* trailsst^a* ft is interesting to note, however, as shown in the last column of Table 19, the regularity in the decrease of the percentage increment from year to year* Welford (192*6) in an interesting paper describes a method for transforming absolute growth curves into straight lines by plotting the lengths at age IT years against the length at age H ♦ 1 years* 8ueh lines may be used for studying growth variation within and between populations, and the limiting length of the species estimated* When the two sets of data for Cardlum edule from Orton (1926) (River Yealra), and from Stephen (1931) (Hunt erst on Sands), are plotted according to Welford*s method, the two straight lines so produced, although there are few points, have the same slope of 0«82t* This indicates that the yearly growth increments decrease at the same rate, althou^i the absolute values are different* The data for 2* raHl&atys plotted in this way, also give a atifi^it line with the sane dope, but until more information is available on growth rates from other localities the full significance of this slope cannot be determined* 1W*

1* The prcfclea and methods of identifying lam llibrenoh vellgers are discussed* as sell as the characters most useful in ide nt i f i cat i on. 2* The veliger larva is described and figured* 5* The fluctuations in abundance of larvae throughout the summer of 1947 have been determined by quantita­ tive plankton isthods which have been described* From this information* an estimate of the length of larval life has been made* 4* The exact lim its of the beginning and enqjbf the breeding season in 1947 have been determined* 9* Preliminary information on the vertical distribution of larvae in P eirlic Channel has been Obtained* 6* A d iu rn a l movement of larvae* being most abundant a t the surface in hours of darkness* has been observed for the area near the Millport Marine station* ?• The organs of the fully developed larva have been described* &* The organs and their development in newly settled sp at ^7 to a length of 1*0 mn* have been described* 9* The changes that occur during metamorphosis are discussed and the three most Im portant changes are considered to be t A* The loss of the velum* B* Hie active functioning of the byasal gland* 6* The formation of the spat shell or dlssoeonoh*/ f*9» The functional significance of these events ere considered* TO* X» scllaatra is found to settle almost entirely on the upper enrfaee of spat collectors* 11* There is a relationship between the angle at th e surface of the collectors relative to the horlsontal and the nunber of spat caught per unit of area* 12# On the basis of projected areas* the efficiency of the collectors increases with the increase in angle* From this it is concluded* that spatting is not a purely gravitational effect* 13* The distribution of the 1946 and 1947 spat falls in the litto ral sone of balloch Bay* isle of Cumbree* has been studied by sampling at various tidal levels on the beach* The distribution and the nunfcers in the two years has been found to be almost identical* 14# The factors causing the type of distribution found have been dlacussed* 15* The rate of mortality of the spat; of the 1946 brood year was found to be nearly 100$ within one year* The poss­ ible factors contributing t o this high mortality have been discussed* 16* The problem of spatting and the selection of a suitable substratum by the larva have been discussed* It has been shown that the needs at the spat and of the adult are different* and whatever power of selection the spat may have is exerted in the selection of an environment/ /environment suitable for Its immediate needs* If that eiivlrannwnt is not suitable for the adult* then m ortality occurs* 17# The rate of water propulsion by adulta 4*5 cm* loag waa found to range between 0*14 and 0*99 with a naan of 0*9 litres per hour in a ten^erature range of 15*0® t o 16, 0 ° c . 18* Hie animal filters approximately 100 times its own volume in one hour* 19* If a ll parts of the g ill are equally eaaoevned in filtering* 1 square centimetre of g ill filters 12*9 cc. of water per hour* 20* The current speeds of water through the two alphas* are different and this prevents mixing of the tvs cu rren ts* \ 21* The g ills are tSiown to be efficient in filtering particles down to the sise of 1 u# 22* The secretion of mucus by the gills does not appear to be a limiting factor in its ability to filter suspended material in considerable concent ration for periods up to 6 hours* 25* Kymograph recordings of S e ll movements have beam analysed mod 1te results compared with those found by ether investigators for ether species* 24* Shell (Adductor muscle) movements have been found to play as part in the spawning set* 29* The method of spawning in both sexes is described*/ 151# X* pullaatra has bean stimulated to spawn both by temperature stimulus and by a chemical stimulus in th e farm a£ a suspension of eggs or of sperms of tbs species* 27# A long latent period and a refractory period during which spawning carnet be induced* have been observed* 28* |« rail la sir a is not as susceptible to stimulation as tbs " oviparous* oysters* 29* Seasonal changes in the goneds of both sexes was followed by examination and study of sections of over 900 mature animals* 38* The sex ratio was found to be approximately equal* 31* Only 0*1$ of the population studied were hermaphrodites* 32* Approximately 0*1$ of the population studied were parasitised by an unidentified species of trematods* 53* Hie length of spat at the formation of the first winter ring varies between 0*4 and 7*0 am* s 34* The mean lengths of samples of spat tram Balloch Bay appear to indicate that a slightly higher rate of growth may occur at the higher tidal levels on this beach* 55* Xn the early spat up to the formation of Blag 2 the largest growth increments are gained by the larger spot* but thereafter the growth lneremssts decrease with increase in sise and age* 3 6 * The method of medal groups from length-frequency distributions of random samples is shown to be net/ 152* /act applicable to £» rmllastra as a means of determining age grows* 37* Harking experiments here Indicated that certain of the rings appearing as surface sculpture on the d& ells at 2* .m llnstrs are valid ae measures of annual growth* 3S# From the marking experiments the annual growth incre­ ment of animals of various ages was determined and cheeked against sim ilar measurements determined in o th e r ways* 39* F ro a $yQO measurements of the length of growth rings on animals from a confined area, a length-on-age curve has been drawn* This curve follows the typical sigmoid fern* 49* The moan monthly increment of growth for the 1947 growing season are shown to follow the temperature curve until the onset of spawning, when there is a deorease in th e growth ra te * L a te r in th e summer there is an inorease which cannot be definitely correlated with a particular factor on the basis of available information on food, etc* 41* The helgit-length and the thiekness-length ratios for various sixes have been calculated and they have been found to follow a simple and direct tangent relationship*

The abbreviations are according to the World List of Scientific Periodicals*

The arrangement is according to the instructions for publication given by the Zoological Society of London*

m Refers to those papers not seen in the original, *53* Allen, w*R*(i9lh)* The food end feeding habits of freshwater mussels* Biol* Bull* Wood*® Hols* 32# (3), *27-l¥* Ataemiya, I *(1928) * Ecological studies of the Japanese o y s te r, With special reference to the salinity o f their habitat©* J* Coll* Agric* Tokyo, J, (5), 333-382* Amemiys, I .(1929) * On the sex-chongo in the Japanese oyster, Qstrea algae Thuriborg. Proo* imp* Acad* Japan, £» 28U. Ashworth, J.( 1904-5). Botes on Tapes pullastrs. Proo. Lpool* biol* Soc* JjJ, 15* Atkins, D*(1936). On the ciliary mechanism and inter­ relationships of 1 araellibrancho* Part 1* Quart* J* mier* Scl* 21* 181-308* Atkins, B.( 1937b t)» Part IX* Quart* J* micr* Scl* 339-373. A tkins, D*( 1937b 0* Part III* Quart. J* micr* 8ci. 375-421. A tkins, D*( 1937c i). Port XT. Quart. J, mler. Sol. 423-445. Atkins, B*(1938a i). Part 7. Quart. J. micr. Bel. 80. 321-329. Atkins, D*(1938b >). Part VX. Quart* J. mler. 3el. 80.

I 331-344. A tkins, 3>*( 1938s >)* Part VII* Quart* J* raicr* 8ci* 80* 3h5-h36*/ 154. A tk in ., 0,(1943). pert VIII. Quart. J. alar. Sol. jfe, 187-25*. Belding, 9.1,.(1912). fieport on the quahnug and oyster

fla h erla e of lu t a d w s s t t i . Conmoawea lth a t Maoa. State print era, Boston, 1-1 A* Bolding, D.L.(1916). Report on tha Clan Fishery. F iftie th Annaal Rep. Com. Fleh. and Oaaa (Baas). Public Boo. jJJ, 93-234. Bernard, V.(16§•). 8ur Xe developpement e t la morphologic da Xa eoquille ohez lee lamellibrenohes III* Anisomyaires# Bull* 8oc* geol* Fr* (3), jjIt* k iM M p Faria* Biedenam* W#(19d)* Untersuchungen hber Bau und Bntstehung der Mollusken-Schaler* Jena* Zeltsehr.ra, 1~l6h* Blegvad, 8«(1f^)« Quantitative investigations of t)a bottom invertebrates in the LimfJord 1910-1927 with special reference to the plales - food* Rsp* Banish hloX* sta* Jfc, 33-52* Blegvad, H*(1930)* Review of Stephen's 1929 paper os ra>nina tenuis Cons* int* Kxplor* Bar* J* Boggild, 0*B*( 1930) • fhe shell structure of the Rollusas* Banalcs Selekabs Skrlfter* 235-326* Burkexsroad* B*»*(1931)* Bex in the Louisiana oyster, fijftBR wiwginio^* Science, 71-72* Chcnberlain* TJU(1927). Thesis* Stanford Library* Coe, W#R*(1932)* BsveXopaeat of the gonads and th e/ fSi* /the sequence ef the sexual phaaea la the California oyster (Oatrca lurlda^ * Ball* . Soripps* Insta* Oc©anogr. tech* Series 3# 119* Coe, W*R*(1936)* Sex r a tio s and sex changes l a aoXluaea* Peleeneer J u b ile e Memorial Volume* Mem* Bus* hist* hat* Belg* (2) Fasc* 3* 69* Coe, W*R* 41 H*J« Turner Jr*(l938)« Development of the gonads sad gametes in the soft shell elem (Uwm jHBHieii)* 23 figs* J* Morph* § g t no*l* Coe, W*R* d Denis L* Fox*(t9Wt)* Biology of the California sea mussel (Mytllua oallfomianus) XIX. Ksvlrom- mantel conditions and rate of growth* Biol* Ball* Wood's Mole, 99-72* Coe, W*R*(t9h7)* Nutrition, Growth and Sexuality of the Flame dam (Tlvella atultorum) * J* exp* Bool*, ao#1« Cole, H*A*(1936). Bxperlmeats la the breeding of oysters f Oatrca edulls) in tanks with special reference to the food of the larva and spat* Fish* Invest* (2), JS, no*h* O de, H*A*(1937)* Metamorphosis of the larva of Petes edulia* Mature# 1,39* M H l i b C o le , H#A*(1938a) * The fate of the larval organa in the metamorphosis of Potass eddis* J* Mar* biol* ANN O J i., 1 2 , n o .2 , W 9-485. €*!•» H.A.(1938*}» A •yetwa of oy«t*r cultur*. Coma. tat. gxplor. >er* 12, no»2, 221-235./ m . Cole, H#A#(1939)# Further experiments la the bm dloi of «M «w In tanks* Flhh* Invest#( t ) f j £ 9 *©#!*♦ Crosier, U#J*(t91h)# growth of the shell la the lemellffrramflii Boelnia diseaa (BaevaK tool# lb# Abi* ft Anett J$, 577-581** Barnes* D#(f935)* I*e ro le dee organism es flans la form ation do® vases marines* Ann# Soc# geol# &elg#9 JJ£f fii3* Devalue* G«(18$2)» Recherches sur la generation dee hultres# Corapt. Rend# et Menu Soc* Biol#* Jfc* « 7 * Davis, F#M#(i923)# Quantitative studies on the fauna of the sea hottest* no»1# Preliminary investigation of the Dogger Bank# Fish# Invest# (London 2) 9 J$, no#29 s . Day* J*H# flk D«P# Wilson (193U)* On the relation of the stihstrstum to the metamorphosis of Boolecelepla XBUfflARfi& (C lap ared e)t J* Mar# b lo l* Asa#

Dodgaon, R#W#(1928). Report on lueeel Purification# Fleh# Invest, (2), 12* no*1# 9n>, Q.A.(18»9e). m m liBilfl&S* bl

nr«6, 1-25* I Tmtwn&a, W .(1 9 3 1 ). O rigin end dOTelopaant of tlw p e r i - j Sardian and k id n e y I n Octree. Pro®, roy. Bo«. , 107. J Field* X«A*( 1922). Biology and econoiaio tbIuo of the cea !' maael, Kytllna ednlle. Boll. 0*8. Bor. Fl#u»

J f i* 187* Flatt«iy, F.V. * C.L. * alt <*.(1922). The Biology of the Eee Shore. Sidgvlek and Jeokeoaa ltd * * Beaton*/ ‘ 158. Vert# £*(1925). to to growth tf some latnellibrenehe la rolutl

ecology of the little neck dam. Pauhla JiSttB tt* Conrad. Trans, roy. See. Can.* (3)* 22* Section T* | ! 2t»9-a69. I ?•} A m t r , C* Hcfcean, A 0 . « . 8nlth«(1 9 2 8 b ) . Hot os on the | ecology Of tho hotter clam Bexldogne irlan nt ana. fj Desheyee. T m a a , roy. Soe. Can.. (3) £ 2t Boot Ion V,i 271-2 8 h . i M ller. J.L . A 8.L. Clarice ,(1936). Further experiments on toe feeding of Calaaua flnnmrahleua. B lol. Boll.

Wood? a Hole.* 2B* ' M le r, JJ..(1937). Feeding rate of 5£lSffl* fiMPWMffM la rotation to eaelroniaental condition*. Blol. k. B u ll. woodPo H ole, jig ./ • a X ta tf f , P .8 .(1 9 2 6 ). Hew indtliodt to SBSSSUrO t)Ml VOtO Off flow produced toy tte giU s of oysters sad otter m olluscs. S cience, J& , 233* Galt e off, P.8.( 1928s). Experimental study of tte foaotlfli of eyater gills. Bull. U.8. Bur. Fish.,

G a ltboff, P*S.(192&>). Experimental study of the function of tte oyster gills and its bearing on the problems of oyster culture and sanitary control of tte oyster industry. U.S. Bull. Bur. Fite., Jill, 1. Gelteoff, P.S.( 1938a). Physiology of reproduction of Ostrea vlrginea. 1. Spawning reactions of tte female and male. Blol. Bull. Wood I no.3, i|£l<4$86. Galt soft, P.8.(1938b). Physiology of reprod Oetrea sirslnea. XX* Stimulation of spasning in tte female oyster. Blol. Bull. wood's Role, JQ, n o .2 , 28d« Galtsoff, P.S.(1940). Physiology of reproduction of Ostrea rlrginea. XXX. Stimulation of spasning la male oyster* Bid. Bull, wood's Role, no* 1, 1 17-135- Gesfee, E*(1875)« Zool. Roc. 1878. m Gltoscn, A.H.(1923). Hydraulics and its Applications. B. Tan Bostrsnd Co. , Res York. j grare, »JU(l9t7fc » • natural history of tsUlnoldcs. Blol. Bull. Wood's Hole, £2, 208*219. i Gray, J.(1928). Ciliary Movement. Cambridge Unis. Press*/ t« 0 . Hagmelop, li{f91<)* 9b op die Ibrl^pflam aog dor Auster vm A A im fiekcllochen Auoternbanlce* Wise* teereeunt. Abt* Helge,,

Hamm, w,( 1909) • Posten&pyonale AntwicklungBgeeehlcht e dep Baleyitdan, Zool, «Tb,» Anst* u# ontog, B£» IB*

H f t , 2 . Heath, H,{1905)* The breeding habits of chitons o f th o California coast, Zool, Ana,, JQ, 390-393, Beoht, S,(t9l€), Tho watop current produced by Ascidia itiii W, exp, Zool, jjg, Keztoere, K*( 19110* l^w icklungsgeeohieht o pen Anodanta oellensla, Schrot* Z, wiaa, Zool, 408» Holmes, S,y,( 1902-3) • Phot otazls in Volwoat^ B iol, B ull, Wood’s Hole, tk$ 3 f9 -3 ^ * Hepfcins, A,K#(1931)# Temperature and the shell movemento of oysters, 0,8, Bull, Bur, Fish,, jg, 1-th, Hopkins, A^B#(1933)* Experiments on the feeding behaviour li! o f the oyster, Octree gjgaa, j, exp, Zool,, S i I* I ■ •* 3 * kS9-iO k» Baskins* A.8.(<935)» Ansehmaat of tte O lym pia o y atsr* j o«tiw lurlda to plttaesurfaoaa. Bodogy, (t), 82-67. Hopklne, A.E«(<936). Activity of tte addaotor munols In ayatar*. Phyeiol. Zoo X.. j. (W » 1)98-907. 1 Hopkins, A.*.{<937). SxperiMental ofcaervations on .pawning, < larval development and netting in the O lppU oyster, \ SmSXSA JJBSUS* 0*8. Boll. Bur. Blah., J ,«n o . 2 3 ./ i « t «

H ort, *#{1933)# Oa H k development of tlio Olympia oyster,

fittWB ticlfll* Carpenter, transplanted from United States to gaps** Bull, Jap* 8oe, eei, Figw, 1, (6), 2*9-276, Hunt, Q,B,(1925), Tho food of the bottom fauna o f the Plymouth fishing grounds, J, Mar, Blol, A s a , &*&,, H* 960-599# J&okeon, B*T»(t8S8), Development of the oyster. Pros, Boston Soo, nat. H ist,, y , Jackson, R,T,(1090)# Fhylogem y of the Peleeypoda, The Arieulidee and their Alllee, Meza, Boston 8oc, net. H ist,, i|, Jordan, H*(t9t9)« Ober die Artf wle Maetra Innate aleh la den Band eiawuhlt* Zool* Jb,, A bt,f,allg, Zool, a» Phyeiol,, y , Jorgensen, 0* Ba*ker,(l9h3)« On the water transport throng* the gills of bivalves, Aota Physiol, Scand,, J , fssej^, 297-3Qlu Jorgensen# 0. Barker. ( 19M£) • I.einBlllbraneh vellgers fro* Deal eh vat era* Repaint from O. Thorawu Reproduction and larval development cf Deni eh marine hottem inverteibratee, with special reference to the planfctoaic larvae in the sound (creaand). Medd. yoc^ Banaerke Pick, a, Havundera.* Serial Plaaktoa, 3d* J , / tfe * iteK&eUmen ana dea Helgolonder Plankton* Meetiasmg ihrer ortsoghhorgteelt durefe Augsuebt# Witi* KMnBoni«pt«f Abt# ffelge#, Jj|y no.5# 1- 6 # JCellog, J*I*#(t903)* Feeding habite cad growth of Venus imtiBSKlS* Bull# X«Y« 8t# Hue. JJ|* Kellog, J*L#(l9f5)# Ciliary raeohaaimo of lamelllbreneho, w ith daoeriptione o f anatoay. J# Morph* * j&» ao#h, 625*701* | Kikudhi, K*(1930)# Diurnal migration of Plankton ernstaeea# j Quart* Rov# Biol#* JJ# j Korringa, P#{t9fc0)# Experiments and observations on sssraing pelcgio llfo and sotting la tho Suroponn | flat orster. festrea adults L» Arch. Maori# Zool.# 2* 1 -a w . |

&&Ww»*ttthiei«.(l69£). Memoir e b u tX b devBloppeaent Oe. (j ii brcnchloa des smU ubqum aoeph.1.. lm»Uibna#K. f I i-m, sel. aat.» i»» S»r.T omb 5 . J Labour, H,V.(1937). Larval ea& poet larval Lin* tr o a I

ttymooXh* S, Mar, B lo l. A b b . 0JU, jgl» ao.2. | 705-710. ]

Labour, *.T.(1938«). Sotee on the breeding of boob .j looellibranehs from Plymouth and their larvae# g* Mar# b iol# Ass* 0#K*» £ 2 no*l, H9-1h5# | la b o u r, M*T*{1933b)* The l l f o h is to ry o f Jg liJfc jf* Mar# b lo l# Aso# 0 #X# # | W M *52. / !

J 1*1111#9 h l« i 8tS« Jhst#(l913)» Breeding habit# of the

heteronereis foam of Moral* UflfefiSS Wood* a Hole* Bass# Biol* Bull* wood1 a Hole* jji# 147-168* I*ooea»off , V*I**(1937)* Seasonal gonadal changes of Hie adult ©lam Venue raercenqria (L) * Blol* Boll* W#odf# Hole, 2 2 , 406-4*16*

Looeanoff, V#L*(1939)* Effects of temperature upon the shell movements of olama, 2* mereeparia* Biol* Bull* wood*© Hole, jg , 171-182. Doosaneff, 7*l»#(l$t|2)* Shell movement* of th# edible snssel Mytllma eduli* (L) in relation to temperature* WOolcgy, J3 , 23t«23b#

Rooeanoff, V*l«* A C*a * Homejkef(1%3)* Feeding of oysters in relation to tidal stages and to periods of light and darkness# Biol* Bull* Wood* a Hole, j£t, no*3* Beven, 3.(1848). Bidrag till Kszmedomen em utvecklingen of V Hollusea Aeeahsls Stockholm VeteAek* Acad# Haadl* for 184ft* Berman trenslstion without figures by Creplin in t

Aron* Meturgesdh*# IS* 181)9* HseBiaitie* £*M*(19M)* On the method of feeding of four Peleeypode. Blol* Bull* Wood9* Hole9 £ 2t n o * i* M arshall* S*H* 4k A*P* 0rr#(1927). Who relation of the plankton to some ehaaleal and physieal factor# in the Clyde see arse* h Her* blol* Ass# 0«X«t JL5# 337*/ ffii* Marshall, 8.M., X ldulii! A A#P#Qrr.(l935). On the biology & JLtiMBB8lliSB^7* Seasonal d istr ib u tio n , else, weight end chemical eoaqposltlon in Loeh Striven in 1933 end their relation to the phyte- plankton* y* Mar. b lo l. Aee. U .K ., 22# 793-828. * Massarelli, 0.(1922). Mote aulla blologia dell oetrloa (Octree edulls h.) 1. Hsolta delle larvee dureta periodo lervale. Boll. 8oo. Met. Mopoli, ill* 191-159. SeVlHi&t H*0.(1924)» the life history end growth of the laser ©lam. state of Washington, Department of Fieheriee, 92. Keiseuhelmar, £.(1901). Bntwicklongeaehiehte von nreigaenaio polymorphs Ball. Z. wise. Zool. f at, 1-45T* *«f* 1-13. 18 JO*. K i ll , H*B.( 18952). The Clyde See Area. Part 1. P h yelesl Geography XXXV, (1892), 641-663. Part 2 , S a lin ity and ehetalcal ooapottllloa of the water. XXXVI, (1892). tfb-729* ?«* 3. Bistribution of temperatures xanm, dm ), 1- 1 6 1 . roy. 8os. Xdin. Mlyaaakl, I.(1935)« On the development of some marine bivalves with epeoial reference to the shelled larvae. J* Fish# Inst* Tokyo, JJl, »°*1« 1-10. Miyasekl, X*( 1936a). On the developtaes* of sema marine b ivalves with epeoial reference to tte flhelled larvae, II. J. Plah. I»at. T<*jr«» J£L. 33-41./ Hiyggeki* X.(19B®0* Qm tte development of bivalves belonging to tte genus, Capbionle* te ll. Jep. 300. sol. Fite, jg, 249-2S**

Mlysgtei, I.(1938 o ). On t t e t e H t p e a t o f T a llin * Juvenalis. Bull. Jap. 800 . sol. Fish., J, 179-162. Hlyasaki, X.(1936b). On tte development of Hiatal is orientalise Bull. Jap. 80 c. sol. Fiah., J, 183-185. IHysstet, X«(l938o). On a substance shite is eontalned In green algae and induces spawning setlon of tte male oyster. (Preliminary note). Bull. Jap. Soo. Sol. Fish. , J2# 137-138. Moore, H.F«(1906). Volumetric studios of tte food and feeding of oysters. 0.8. Bull. Bur. Fish., jgfi, j 1297-1308. Morgan# T«H.(l9tO) . Cytologies! studies of eentrifuged eggs. J. exp. Zool., J}, 593. Morse, £*8.(1915/* Observation® on living SSlSm m t fyfriffp and borealis). Biol. Bull. Wood*s Hole, &• 261-381. Sorteaaan, T&.(1921). etwSlao at' m o dtewlopmsat anfl larval fans of G.E.C. Osd, idwnlwTa, 366. Momeop, BJU(1921). *te rota of Breath ef tte eea musaal , (H X LilM "**11* *») ** 8t* Andravs, *.Bt O K *, *. 8 j in Hud.fi Bay. Trans. Soy. Ca. test., 15, tDnnta ■oeaop, B»K»(1922). The r a te o f grow th o f th o eee ouaool ClZSllSE S&&U) St. Andrews, If.B| DUfby, S.Sj and in Hudson Bay* Studies from the Biological Station*, Biological Board of Canada, 4 5 . 22, Toronto* Headiert Alfreds, B*( 1932). Sex reversal in Oetrea v lp g ln lc a . Conte* Canad* Biol* (a e rie * A ), J , 285* Keleon, T*C*(l92t)* Report of the Dept* of Biol* of the JUJ* Agrie* Coll* Exp* St at* for the gear ending June 30th, 1920 (1921), 317. Welson, T.C*(192A) ♦ Report o f th e Dept* o f Biol* of the H*J* Agrie* Coll* Exp* St at* for the year ending

30th June, 1923. (I Heleon, T«C*(1928a), Pelagic dieeoconohe of the common mussel, llytilua edulla. with observation* on the behaviour of the larvae of allied genera* Blol. B ull* wood1 e H ole, J55, 180-182* H eleon, ?*C*( 1928b)* Relation of epawning of the oyster to temperature* Ecology, 1J*5* Heleon, T*C*(1935)* Water filtration by the oyeter end a new hormone offset thereon* Anat* Reo* (s u p p l,i),

88 * | Hewconfee, C*L*(l93$a), A study of the community relation­ ship* of the eea mussel, Mytilus jffliUft* Boology, & ( 2) , 23*~2k3. j Heweontoe, C*I**( 1935b) * Certain environmental fa e t ora o f a beach in the St* Andrews reg io n , H*B*, w ith a preliminary designation of the intertidal eoflnonitlee* ! j . K co l., 33U-355* 1€?. Hewcombe , C #L.( 1935c) • Srotth of Mya arenarla L. la tte Bay of Fundy region. Canad. jr. Baa. JJ ( sec.B) # 97-137. Bewcoaibe , C,L.( 1936a) • Validity of concentric rings of Bya arenarla L. for determining age. nature, 1 3 2 {5 k 57) 191-192. Bewconibe, C,L.( 1936b). A coraparat ive study of the abundance and the rate of growth of Hva arenaria L. in the Gulf of St. Lawrence and Bay of Fundy regions. Ecology, 12#" 8»*5» J u ly 1936. Odhfter, B. Hj«(t912). Morphologie und phylogentleehe Untercuchungen uber die Bephridien der Lamellibranchien. Zeitschr. f. wisa. Zool., i(& , 287-391, kO Ahh. Ohdner, B.B$.{1914) • Botisen u ber die Fauna der Adria bel RoUigno. Beitrage sur Kenntnis der mariner Bollusken fauna m Rovigno in Xstrien. Zool. Ana. 9 2j&, no.h, 156-170. Orton, J*H*(1912). The mode of feeding of Crepldula with an account of the current producing mechanism in the mantle cavity, and some remarks on the mode of feeding in Gastropods and Lamellibranchs. J. Bar. blol. Ass. U.K., U.S., 2, W k-k7S . O rton , J.H.{1913). The ciliary mechanisms on the g ill sad the mode of feeding in Amnhloxue. Ascidlans and fie'LflMSSEB toga^a. J• Xsr. hiel. Asa* U*K.,

If.8., Jg, 19-h9. Orton, J.H.(1923). On the significance of rings on th e «h«ns of Cardium and other molluscs. Xature, July 7th, 1 6 ft. 0»ton, JJU(l9ftS). on the rate of growth of Cardium aM a.

P u t 1 . Experimental observations. J . B ar. blol. Ass.. 0.S, jfc, no.2, Aug. 1926. Orton, j.h.(1927«). A note on the physiology at sex . and sex-determination. J. Bar. blol. Ase. U.K., «k, 1047-1055. Orton, J.H.(1928). Observations on Patslla vnltmta. Pt.ZZ. I Rate of growth of ahell* J* H er. blol* Ass* ll*K*(n*e*) i 868-87U* i Orton, J#H«(1$55)« Observations and experm on the sex-Changes in the European oyster* Pt»XXI* On the fate of the unopawaed ova* Pt. XV* On the change from rale to female* J# Bar* blol* Ass* U*K* JJ, 1-55. Orton, J*R*(1936). On Sex-ehange in the oyster, StMtES&k L* Part 5* ^ simultaneous etufly of spawning in 191? in two distinct localities* Bern* Hus. ray* Hist. get. Belg.(2) Pass. 3, 997-1056. Orton, J.H.(1937a). Oyster biology and oyster culture. The Buekland L ectures f o r 1935* London. Edward Arnold and Co. Orton, J.H.(1937b). Son* Inter-Relations between bivalve *pst-falls, hydrogrephy and fisheries. Xature, i]|Q, 909-906. Parker, O.B*(l9l4). On the strength sad the volume of the water current s prod used by sponges. J. exp.

X*e9U, Jfi* 4434/ m , F«fc, R.H.(1877). Tha minute structure of the gills of laoellibranch molluscs* J. raier. 8ci.(a.s.), JJ. * Peleeaeer, P.(1892). Introduction a l fEtude dee ilolluequss. A ah# See# aool. Bslg. jJ2, Bruxelles* Perkins, R#B#(t931)« A study of oyster problems in Bamsgat Bay during 1930* Report of the D ept, of B io l. B#J* Agric* Exp* St at# yuly 1st 1929-Jhne 30th 1930. Petersen, C*G*Jotu(l915)* On the animal communities of the see bottom in the Skagerrak, the Christiana Fjord

and the Danish waters. Hep. Danish Biol. St a., <22 * Psytherch, H.F#(193W* Role of copper in the setting, metamorphosis and distribution of the American oyster, Ostrea wtrginlca. Eeol. Monogr. , J|, no.1. Qusyle, D.8.(19t*3). Bex, gonad development and seasonal gonad changes in Paphia stam ina. Conrad. J* Fish. Res. Board of Canada, j|, no.2. Hanson, G»(192<). Be Filtration de l'eau par les lamellibranches et see consequences# Bull. Inst, oceanogr* Monaco, no«b69, 1. Hice, E.I*.(1897). Die systemetiche Verwert harkeit der S»iemen bei den LamelllbranchiatSfii. yens. 2# Weturw*, 3 |i 2H9* Rice, E*I**{ 1905). Bote© on the development of the g ill in ifyjflftfflV S cience, ( n .s * ) , 2X* no#53R# 577-378# R ic e , E#L.(1908). G ill development in m ttiiM * Biol. Bull. Wood* a Hole , J||» no. 2, 61-77#/ t m Sic#, «.L.(1930) * Fusion of filaments in the lawllibrm oh gill* Bid* Bull* Wood*© Hole, jg. Ride wood, W.G.(1903). On the structure of the gills of the Le*a<brmiehia. Philos. Trans. (B), 125, 1h7-28h. B ose, H*( 1925) . Contribution a lf etude de la biologie da plankton. La problem© dee migrations verticelee jouraalieres. Arch* sool. Univ. Coinfcre., 387-524. Boughl#,, ?*C«(l933)« The life hletoujr of the Australian oyster, £. ootauieroigila. Proe. Linn, roe*, 52 )« Ester Wax: a new enfeedding medium. B a tu ra , 136. 121* Steadman, K*F.(l9*t?)» Ester Wax: A new enfeedding medium. Quart* J. mler. Set*, 55. 123-133. Stephen, A*C#(192d). Botes on the Biology of viinn* tenuis da Costa* J* Bar* bid* Acs. t?«K«, JJ, no.2. Stephen, A*G#(1929}* B otes on th o r a te o f growth of y . n i t ^ |j jyggllH da Costs, in the Firth of Clyde# J. Bar. jj b id . A©o. (n*s.), »**1* 117-129. Stephen, A.C.(1931). Hotee on the Biology of certain Inmellibrmadba an the Seottl«di Coast. J. Bar. b i d * Ase* U*K*, S2* ao*^* S tephen, A* C*(t93£)« Botos ou the Ridogy of eras laaellibrsnoho in the Clyde area. J. Bar. blol. A os. U.K. (n*e*}» i i (1)t 91-68*/ S td l, E#(1937)# Bectoachtungen tiber die Fortbewegung bei •iaigta grabenden Musoheln# Rev# sulsse# Zool#, l i t 385-390# Stoll, 8,(1958). S xaej/t le mode de locomotion de que^ues raollueques marine. Trav# * Eta. blol. Roscoff. f 3 2 , 3- 29 . m Talt, J«8#(1957). Fish# Scotland, Sol* Invest. (Ho.1). Thiele, J*{1935). Handbuoh der 8 yet emat Isohen Welehtlere Kunde# Fleohen, Jena# J. Thompson, S ir, B'Arcy W.(19U7)* A Glossary of Greek Fishes. Oxford University Press# Thereon, G#(19U>)« Reproduction and Larval development of Danish Merino Bottom Invertebrates, with special reference to the Planktonlc Larvae in the Sound# Xedd* Beam# Dszuaarka Fiak#-og Havundera, Series Plankton, Bd# k$ Kobsnhavn, 19W>. Trueman, B*R*( 191*2) • The structure and deposition of the Shell of J&XBX&2* J* ®ior# Soo#, JQ£, 69-92. SSellanee, X*(1892)# Recherches our la filtration de lfesu pur lee mollueques et applications a l fOstreiculture e t a l*Oceanographle. Corapt. Rend* e t Mem# 8oc. Biol* J ||| (2) , 1386# Vies, F.(19C4*)# Locomotion de la Rucule# Bull# 8oc. sod# Fr# T. 52#/ ITS* Wolford, W ,(U ^ ), a new crephle method at «M M rtkU «

tte crcwtfc a t m lm ls, »iol. Bull* wood'* Bole, Jfi. Wesserlooe, B*(l9t1) . Hie Entwicklnng der ^j^tyn bei Crclaa

i eoraae endam Aeephelen dee Soason Wamere* Zool, A* Bd. JL, B f t „ 2 . »ehh, U.E.(193») * An apparatus for records the valve movemente and the extrusion a t dejecta of oysters. * . Cone# in t . E x p lo r., % ( 3) 9 361*362. Welch, P.S.(t935)* Limnology. MoBrew H ill, H.T. 1935. Werner, B. (1939). Cher die Entwicklung und Arten t«fieh 0l t a | r m Mueohellarven dee Bordaee planktons, unter basonderer Beruckeioht igung der 8 ohalentwieklung. Eool. 2b#, A1)t« Anat., Haft. 1.# 1—5^1, Jait* j Weymouth, F.W.(1923). The l i f e history anqferowth of tha Pismo clam (Tlvella atultoriiia) • C a lif. F lah Game Bull. Ho. 7, 120. Weymouth, F.W., H.C. KcMillln, H.B. Holmes.(1925). Growth and age at aturity of t2»e Pacific razor dam, filllcma (dixoa). 0*8. Bar. Fish. Boa. no.98U, Jft, 201* 2 3 6 . Weymouth. F.W., H.C. XeEillin, W.H. Rich. (1931). Latitude and r e la tiv e growth in th e razor class. Bilious jggjjflg, J. axp. Biol., & Wlnekworth, R.(1931). On the growth of gJBBttUl BMtflftfl ( Yeneridae). Proa* Mdeool. Boo. Lond., 115-116. Wilson. B.P.(1936). Tha development of the Babellld, 171*. Wilson, P.P.(1937)* The influence of the substratum on the metamorphosis of HotomaatUB larvae. 2. Her. b id . A ss. (n .e .) , £ g f 227-243* Wright, F^.(1927). A report on the Cockle beds and Cookie industry of England andWsles. Fish. Invest. Series II, .2, no. 5. Tonga, C.M.(1923)« The mechanism of feeding, digestion and assimilation in Mya. Brit. J. exp. Biol., £ f 13-64. Yonge, C.M.(1926). Structure and function of the organs of feeding and digestion in Octree edulis. J. Her. M ol. Ass. U.X. 14. 295*336. Tonge, C.M.(1937). The biology of pea-Pellcanl(L), and A. serresiaaa (Midi). J. Mar. blol. Ase.(n.s.), 21. no.2 , 687-704* Tonge, C.M,{1947). The pallial organs in the Aspidobranch Gastropoda and their evolution throughout the Molluscs. Philos. Trans. Series B, no.591, 232. 443-513* Tonge, C.M.(1948). Formation of siphons in Lamellibranchia. Mature, 161 no.4084* Ziegler, H.E.(1835)* Me Entwlckelung von cornea Lam. (S uhaerius sgeagBa B .) . z. wi*s. Zool. Bd. JH, 525-569. Zobeli, C.S. * W.H. London.(1937). The bacterial nutrition of the California mussel. Proc* Soc. exp. B io l, and Med.

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:-■'■■■■.* ..':.:L& &i-.k , ' • - W ' ■-.•■»■' : v^-: •; ::■ ■ f’ -v:^; ? .,- %. -.’.Vi: ■ ■- ' V": H.';/ ! f’-'•'; ' s;: '/V'3' *■ Tt,'- pv, •*■■< ffc* litw etor* on digging mavamvta of lamlU« branch* is not extonaivw end other than the work of Srow C<906) oa S nala directive and Jordan ( 1915) on Mactr^ Inflate a thaw la little of significance until the extensive investigations of Froenkel (1927) on th e Solcnldco# Later, Stoll ( 193®) » gave brief description* of methods of locomotion in various species* Drew (t » 8 )t Horse (1913)» V ies (1901*) and S t o l l (193®) here described locomotion in various protob ranch*• Of all lamelllbranehs, the Solenldae lend themselves best to a study of locomotion because they are probably the most active and rapidly burrowing, and it le possible to induce movement of the foot by stimulation (Frcenkel, 1927) « This is in^oeslble In species ouch as uollastra in which almost any type of stimulation causes immediate contraction, generally accompan­ ied by closure of the shells* While the nerve-muscle physiology of movement in gallsstra was not studied* the general pattern of digging movements was observed and the results may be of come interest*

W h e n oullagtra is removed from its burrow and is allowed to stemeln undisturbed for some tiraa on any surface, the shells open and efforts are made to burrow* If the ssfc stratum is too hard fen* the foot or the shell to penetrate, horizontal movements result; but if the substratum is soft enough for penetration, then the seas/ 8» /m m sequence « f movement® a l l am themiaal to ^wct* Bale** the aaiael 1* ®eveThera 1* an affinity for crevices, or against overhanging roots whose has* i* buried deeply enough* Moot animals are burled an inch or two below the surfaee* bat a imTiber may be found with at least part of tb* ttom iag «aA turnm ? hav* Poaatoaero* trlouatw growing oo xmq» la nature the orientation 1* variable* The animals lie with the tranever** andlosgitttdlnal axes in Tsriea* planes# when they are allowed to borrow into pare wand they assume a position with the dorsal margin of the shell nearly parallel with the surface*

The digging aovwsen&s hare been observed many time* in all else* of animal* from the youngest spat to the largest adult in sand* rand, gravel, powdered glass and on flat surface** Zn every ease, regardless of the position and the environment* there was an inevitable sequence of nwvewents* 3 t B eing th e medium o f send, in which th e movements ere heet executed, aeauraing the animal to be iofcedded Just deeply enough to prevent It m iii« ever, sad n th the long axis parallel to the surface of the eand; the sequence of movements la as follows: 1* The valves are opened# 2# The foot is protruded, pointed with a probing motion* This baeic and forth searching motion is continued until the foot la fully extended* The tip of the foot may extend to a length equal to that of the animal# The degree of vertical penetration in this phase any vaxy considerably and ia partly dependent on the type of substratum* (Pl#50, fig#a)« 3# The heel of the foot is protruded vantrally# (PUS®, flg#b)# Um The heel expands both laterally and posteriorly, so that, eooyled with the anterior extension of the foot, m anchor is formed# If the tnftstretua is firm enough, the f oot maintains this position and the shell moves* 9# The valves open slightly. 6* The two siphons! apertures close, and the adductor muscles contrast reducing tho volume of the mantle cavity fore&tt out the excess water in a stream from the anterior end Jest below the adductor mosaic# Presumably the curtain maintains a seal around the foot and the remainder of the mantle edge during this operation*/ k . Almost immediately the aaltrior pedal w tm to w contract and the posterior retractors relax, causing the anterior end of the shell to dip down and the posterior to rise upward* It is prctoable, and this deeerlption of the play of the mueeles is only conjectural, that contraction of the anterior retractors la confined to that part near Its Insertion into the shell. (Pl.90, flg.o). 7* The final movement now takes place as the shell moves forward and down* The foot remains in Its position of anchorage and the more distal portion of the anterior retractors now oomes Into action end the hody Is drawn forward. At the same time elements of the posterior retractors running downward and forward to the baas of the foot contract, so assisting in the movenmixt* (P1.50, fig.d).

In Plate 90 the lines 'XX* and VT7V are vertical sad horlsontal reference lines respectively. In figs. b, C and 0» the foot is In relatively the same position and the shell and body have moved in relation to this. The figures are diagrammatic* This sequence of movements is repeated until the animal reaches the required depth* Kymograph record­ ings, an example of which Is shewn in Pl»3b flg.5» substantiate the analysis given above# The recording reads from left to right end the kymograph arrangement was snob that a downward movement of the animal is Chown in an / /an upward n o rm »xxt of the tracing pen* The attachment of the d o ll was on its anterior lateral area, so the flnxinm downward movement l a recorded* I t la d i f f i c u l t to compare the kymograph tracings of digging noremande In X* pullawtra and In Solen (Preankel, 1927) • fop the latter wae held In a clamp and wortleal movements of the foot r o o a r d e d * - In the treeing Pl»3t|> fig* 3# will be not lead a alight dip of the pen loot prior to the long upstroke* This la Interpreted aa a alight relaxation of the adductor muscles, allowing the valves to gape slightly and in thla dagr loosening the aand around the shells* Then follows th e sharp upsweep o f th e pen showing th e downward movement of the "nose* of the animal {Moweaaent d)f (Pl*30, fig.a)* The "nose" Tory rapidly tips up age In allowing the pen to drop* T hla upward movement slows down in i t s l a t e r stages* and the beginning of the next sequence may he under way before the animal has come to peat* ae shown by the horison- tal lines In the first few sequences of PI* 3k* fig * 3* One wertlcal sweep of the pen up and down* plus the following h&rlsontal line* constitutes a sequence* This tern la analogous to the "Grabetufe" of Frsenkel (1927)* T h e Initial probing of the foot he terras, "Grabeehrltt", and a nusber of «Grabeehrittw form a "OrSbatufe*" In turn* a nunhar of Torabstufe9 form a "Grdbperiode* * which presumably ends when the animal reaches therequired depth «*

In the doneription of IfovesMixt€ is mentioned the stream of voter tlio t is forced out of an anterior

separation of the pcH ial curtains* The valve closure responsible fo r th la la not represented cm the treeing because it appears to be ooineldent w ith the downward move­ ment* of the *nosew, end ae closure of the valves would resu lt in an upward movement of the pen* the two movements are no doubt incorporated* The purpose of thla current has been interpreted, firs t yb B re w (1906) f o r K u a la qiraetua« and la te r hr Jordan(1915) fo r Maetra in fla te -

P r a e n fc e l (1927) fo r the solexxidae, and S to ll 1937, ( 1930) fo r savors! lam ellibranehs, as earring to loosen the sand

in front of the animal to allow easier penetration*

Certainly in X* rallantre the je t la pow erful,for a considerable disturbance ie created in the oaad even when the animal is at some depth* There appears to be no good reason to doubt the interpretation of the above authors* An a n a ly sis o f s i r Kymograph recordings o f digging I. movements, given in Table shows that once digging has begun, the average tim e fear each sequence is 2*42 minutes*

The averse* xswxher o f eonseoulivs sequences17# is a n d t h e naan extent o f the in itia l downward movement is 1*8 an*

The effective downward movement is appreciably leaethsa th is due to the lif t of the anterior end in the second phase of the Bequenoe, but the extent is variable depending on the type o f subetreturn* Horizontal More-ant./ D»VI . . 1 0 w (

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When 7* pollastra la first placed in an aquarium toah with suitable substratum# tbs first reset Isa Is to burrow which it does rapidly* During the first period of darkness* however# many of the smaller aainsls return to the surface and move about considerably* as shown by the long furrows out on the surf see of the sand* Whether there is aa actual * darkness1 of foot is debatable for the animals m y here returned to the surface la any tn atf but this point was not investigated* The travel nsvemaot is seeoiapllslKed by the sane sequence used la digging# except that the Initial dip of the anterior eat is aot sc extensive* If the sand is very loose ©any of the larger animals have difficulty in obtaining the in itial anshorage for the anterior end of the shell* That la* once the *aose* of the clam is buried* the rather flattened Imole region forme a pressure plate# and the weight of the sand on it holds It steed? as the posterior end is polled deem* If the initial anchorage is not obtained the anim al will plough along the surface for some distance before the ”aoee” g a ts a grip*

It h£* been shown that the digging movements consist of strict and underleting sequence of movements* which involve fine ^rodhrcmisat ion of the adductor muscles* the retractor saisdes end the muscles of the foot* The role of the blood system in contributing to the pedal/ §» /pedal activiti m has 1101 been investigated# Drew (*»90d) ««& 9VN8M (?927) have shewn that the blood assists la pedal movements, bat tha latter author has shown that blood pressure plays only a minor role in aris«a to the o&soulatare in inducing changes in the fora of the foot# Sumter, in £» m llastra* there la not the rapid had extensive changes anoh as occurs In Solen. and the extension of the tip and heel of the foot forma an anchor, rather than the exclusive sm iling of the tip as In aolen. fhe stimulation which oaueee burrowing has not bean determined, other than that it occurs whenever the animal is burled# \ Also, shat is the stimulus which senses the animal to stop burrowing? Fraenkel believes it la net necessary to assume a nervous inhibition, but that the cessation of digging movements occurs as a result of fatigue, but this is hardly likely with pollastra. which w ill burrow repeatedly, though the period of shell closure mused by the removal from the sand may serve for recuperation* However, the amount of muscular activity in the two species Is hardly comparable, nor is the time required for burrowing# Praenkel (1927) found that Solan orientates Itself in a direction which corresponds approx­ imately to the direction of the resultant of the centrifugal force and the force of gravity* X* raftl&etra may be found orientated in nature in nearly every conceivable manner#/ f* file same applies t e their orientation in an aquarium with a homogeneous substratum such as sand* Uo experiments with centrifugal ftn t war© triad* Sticxastions of the siphons and auntie i n j * raillaatrft invariably cause shell closure* Similar atiaala- ttcm In Bolen. according to Ifreankel (1927) » n early always Initiates digging movements* and he dot ©mined hy sllniaa~ tlsn experiment® that the visceral ganglion plays an lagttrtant rale in the release of digging movements* hat the osrshral ganglion was ascertained to ho the actual nerve centre for the movements* with the different offset of mantle an&i siphons! stlmolatien, it soma ho interesting ts lawestlgrt* nervous control of the movements in 2* aa lla a tg a . SOME ASPECTS OP THE BIOLOGY OP VEEERUPIS PULLASTRA (MOHTAGU) •

By

D.B. Quayle

Volume I I

P la tes

A thesis presented to the University of Glasgow for the degree of Ph.D. May, 1943. ZI&JlA* of F ig u re -f* Larva just out, the straight hinge stage* 168 u* x ti*h w*

F ig u re 2* Larva* Early un&o* 20k u» x 180 u*

Figure 3* Larva just before metamorphosis 260 u* x 22(0

F ig u re Internal view of right valve of a veliger Showing the hinge area and teeth* 250 u* x 238 u*

F igure 5 Hinge aresjaf right valve of larva* 227 x 209 u* Internal view*

F ig u re 6 Hinge area of left valve of larva* 227 a* x 20F m* Internal view* PLATE I SifaifeSSL.is* Figure 7* Photomicrograph of complete veliger from the left side. Length 2i*0 u.

Figure 8* Photomicr ograph of the external view of hoth valves of a veliger, 225 u. in len g th . Prod* 1 i s the lig h t wnrlnged area inside the hinge and usfco.

Figure 9. Photomicrograph of the internal view of hinge area of the right valve of a veliger* showing the hinge teeth and ligament, x i|0u«

Figure 10. Photomicrograph of the external view of the left valve of a spat 0.% ms. long by 0*35 high*

Figure 11. Photomicrograph o f the external view of th e rl^fct valve o f a sp a t 0*3 am. in length. Vote the difference In density between Prod. 11 and the dlseoconeh* PLATE 2

FIG.7 FIG. 8

FIG. 9

FIG. IO FIG. II P la te 3. Map showing L ittle Cunibrae Island and Great CuBlbrae I si and, with some of the landmarks and Stations mentioned in the text. The 10 and 20 fathom depth contours are shown.

i s m s * A - Location of spat sampling stations* B - Keppel Pier. C - Shore pumping Station on Keppel Point* T> - Plankton Station off Keppel Pier, August 26th-28th, 19h7. £ - Approximate location of the Lion Bock* P - Sampling Station for V ertical S eries, August 22nd, 19U7* Or - Hunt erst on Perch. 8 - Location of Cross Houses Beach* PLATE

23

GREAT CUMBRAE ISLAND BALLOC til BAY *55

CL'ASHFARLAND POMT/ IO

KAMBS BAY / po& MILL PORT .BAY FAIRLIE CHANNEL

II S I FAR L AJSlD" POIN T.

■BG

20

LE CUMBRKE ISLAND

THE GUMBRAES m s u U b Graph shot/lng the seasonal variation in the mnhe? a t larvae as shown by prop easgiles from Keppel Pier ant Keppel Point during the breeding season a t 1W?* The mean wea&ly temperatures at the surface at Keppel Pier, ana the tidal series Tor the period, are shown# The temperature data was supplied by the «* and the Tidal data is from the Admiralty Tide Tallies, I9h7* NUMBER OF LARVAE TEMPERATURE ©c HEIGHT OF TIDE IN FEET 0 4 0 2 60 0 8 0 2 0 3 UY UUT SEPTEMBER AUGUST JULY IO 0 2 0 3 20 0 3 20 LT 4 PLATE 30 Graph showing the number of larvae in jraarp samples of 2 cubic metres, taken at various depths down to kO metres, from a Station in Fairlie Channel, August 22a&* 19^7* Data from Table 2*. PLATE 5

CM

•O DEPTH IN METRES DEPTH

fO

CM 3VAUV1 JO a39WDN P la te 6» Graph showing the number of larvae per 2 cubic metre# of pumped water from the Keppel Point Shore Station, lLth-16th August, 19^?. The period® of darkness and the rise and fall of the tide are shown* Bata from T able 3. PLATE 6 TIME TIME IN HOURS MOO MOO 1900 0300 IIOO 1900 0300 1100

133J M 3011 JO 1H0I3H 3VAUVT JO UJSmnN Graph showing the nurrfoer of larvae from 2 cUbic metres of pumped water from a Station off Keppel Pier in Fairlie Channel, August 26th~28th, 19h7* In addition are shown the rise and fall of the tide and the periods of darkness* The broken line represents the 12 metre samples, and the solid line the surface samples* Bata from Table k* NUMBER OF LARVAE HEIGHT OF tlDE IN FEET 200 120 ISO 40 80 1200 1800 EID F DARKNESS OF PERIOD 0 0 4 2 0 0 6 0 IE N HOURS IN TIME 1200 1800 EI F DARKNESS OF D PERIO 02 0 6 0 0 0 4 PLATE 1200 Eiau udk. Graph showing the nuriber of larvae per 2 cubic metre* of pumped water from the Keppel Point Station, August 29th to Septeidber 6th, 19^7» $he period* «t darkness, and the rise and fa ll of the tide, are shown. Bata from Table 5# NUMBER OF LARVAE TIDE LEVEL IN FEET 300 200 IOO 400 150 50 A U G .AU 2 9 G . 3A 0 U GSE . 3 I P TSE . I P T .SE 2 P TSE . 3 P T .SE 4 P TSE . 5 P T . 6 EID O DARKNESS OF PERIODS LT 8 PLATE to ,.I,? . a. a. - anterior adductor muscle# a. p. - apical plate* b*g* - fcyssal gland* 1>.gr# - byssal groove. c.g* • cerebral ganglion* d.d* - digestive divertieula. f • • foot • g.s. ~ gastric shield* i.g* - inner gill. i.l. - intestinal loop* k.s* - crystalline style sao* mo* - month* oes* - oesophagus* o*f* - oral flap. p.a* - posterior adductor muscle* p*g* - pedal ganglion. r . - rectum* a* - stomach* s t . - statocyst. U. - URfcO. v.g* - Visceral ganglion, v.l* - lobe o f velum*

Figure 1h* Semi^diagraranatic reconstruction of a fu ll grown larva from sections# whole mounts and from the living animals, x hOO* PLATE 9

d.d

k.s.

fxa. aa. s.t.

eg. b.g r:

mo of.

FIG.14 P l a t e 1 0 . . &

Figure 15* Frontal section of a larva to show the relationship between the various organs x I4OO.

Figure 16. Slightly oblique cross section of s la rv a to show the re la tio n sh ip o f the variou s organs x 300. PLATE IO

Siii1 FIG.15

FIG.16 Pla&LOl* Key to lettering* a.a* - anterior adductor muscle. a .p . apical plate area. a * r. anterior retractor muscle. c .p . g . - cerehro-pleural ganglion. e .g . cerebral ganglion. d .d . digestive diverticula. e • p. mantle epithelium. g . 1^* - larval g ill filaments. i.g * inner gill* J.nup. - mouth - palp Junction area l.p * * lower palp. m*e. mantle edge. rao. mouth* o es. oesophagus* oes* ep*- oesophagea e pi the lima. p .a . posterior adductor muscle• u*p. upper palp.

Figure 17. Sagittal section through the right side of a larva showing the g ill filaments x tyf5+ Figure 18* Sagittal section through an 0*35 Hsn* spat* to show th e deeply sta in in g m ultinueleate tissue of the apical plate area in relation to the cerebral gan glion , month and an terio r adductor muscle* x 1000* Figure 19. Sagittal section through the mouth region of a 1.0 ma. spat, to show the lower palp and its relationship to the mouth region x 6 0 0 . Figure 20* Sagittal sect i on through the month region of a 1*0 b i z i * spat, to show the division,and the attachment between, the lower palp and the lip of the mouth* x 600. Figure 21. Sagittal section throu^i the month region of a 1.0 am* spat t o show the upper palp and month and the proximity of the g ills x 500. PLATE P i s t e 12. to latter^nir. a .r . — anterior retractor museles. c .p .g . • cerehro-pleural ganglion. c . t r . — ciliated tract. d .d . • digestive diverticula. e*p. - mantle epithelium. i»S* — inner g ill. l.p * • lower palp. m .c. — mucus c e l l s . m .e. a m mantle edge. mo. - mouth. o es. - oesophagus. u .p . - upper palp. v.m . visceral mass.

F igure 22. Frontal section through the mouth re g io n o f an 0.35 sm* spat, showing the mouth and the upper palps, x 320. Figure 23. Cross section throu$* the mouth region of an O.U mm. spat, to show the lower palps x 300. Figure 2!t. Cross section through the mouth region of an O.h s b u spat, to show the upper palps x 300. Figure 25* Brewing of a whole mount of the upper and lower palps of a 1.0 mm. spat. The view given is frontal, looking directly into the mouth, x UOO. PLATE 12

FIG.22

FIG.23

FIG.25 P la t e 1 3 . ley to lettering.

c . - c ilia * e«p* mm mantle epithelium. m»l* m . muscular lobe of mantle* m .s. - muscle strand* n. - nerve* p .e . • periostracum. P*-l* - secretory lobe of mantle* p »l.su • p a llia l lin e rmiscl es. p.r,nu pallial retractor muscles She - sh ell* B .l. mm sensory lobe of mantle*

Figure 26. Cross section of the mantle edge of a larva to show the two mantle lobes present at this times x 1500*

Figure 27* Cross section of the mantle edge of a 1*2 ran* spat, to show the three mantle lobe8 and the siphone1 retractor muscles, z 4t50« PLATE Key to the lettering* i . g . — inner g ill. m. - m antle. ®» e * - mantle edge. m.f . mantle fusion. m*l. muscular lohe of mantle. m.8. — muscle strand. p .a . - posterior adductor muscle. P*e. • periostracum. p*l* - secretory lohe of mantle. p.r*m. - pallial retractor muscles. s . s . mm siphonal septum. s i . t . - siphonal tentacles.

Figure 28. Frontal section of an O.J* mm. long spat* to show the form ation of the siphons 1 tentacles. Section is through the mid- lin e . x 700. Figure 29. Drawing of a whole mount of the right posterior ventral mantle region, to show the formation of the siphonal te n ta c le s and the g i l l s , from a spat 0 .3 0 mm. x 1*00. Figure 30. Internal view of a whole mount of the right posterior mantle edge of a spat 0.75 nm. in length, to show the siphonal tentacles. Stained with methylene h lu e . x 250. Figure 31* F rontal se ctio n at an 0.3 spat, to show the fusion of the mantle x 350* PLATE E la ls-1 5 ‘ tor.,ta itftertMr a* *. anus. e*P* mantle epithelium. . e .s i* — exhalent siphon* f* foot* i . g . * inner g ill. sue* - mantle edge« m»s* — muscle strands. m% t • - m antle thickening. p»a, posterior adductor muscle p*e* «• periostracum. p .l.n u — pallial line muscles. r* * rectum. B .l* 9 secretory lohe of mantle. a s. - sip h onal septum* 8*t« <* sensory tentacles. s i . t . — siphonal tentacles. v .g . visceral ganglion.

Figure 32. Frontal section of an 0*35 spet at the approximate level of the anus, to show th e siphonal ten ta cles* the exhalent siphon and the siphonal retractor muscles x hOO. Figure 33* Frontal section of an 0.^5 *an*. spat, cut at the approximate level of the mouth, to show the exhalent siphon x 300. Figure 3k* Braving of a whole momt of the posterior region of a 1*0 o b i . long spat, to show the ftiihonal septum and the siphonal tentacles. Stained with methylene tin s x 170. PLATE P la te 16 * Key to lettering. c . - c i l i a . d« d. digestive diverticula. a . d . d . — duct of digestive diverticula e .p . — mantle epithelium. f . — f o o t . i . g . - inner gill. i . g . o . origin of inner g ill. k . kidney* k .s . mm crystalline style sac* m. - mantle* m .e. - mantle edge. s u l. — muscular lobe* m. t * - thickening of mantle. 0 3 . - osphradium. o e s. oesophagus. p .e . - periostraeum. P*l* secretory lobe. P * r. — posterior retractor muscles. r . - rectum. s . - s t cmach. V .g. - visceral ganglion.

Figure 35* Frontal section through the posterior re g io n of an O.l* swu spat, showing the gill origin z UOOe Figure 3 6 • Frontal seetion through the posterior dorsal region of a 1.0 nan. long spat, to show the specialised epithelium which is described as the osphradium x I4.5 0 . F ig u re 37* Frontal section th ro u g h a 1 .0 ora. long s p a t, to show the relationship between the gills, m antle and siphonal retractor muscles z 50. Figure 38* Frontal section, through an 0.35 »«• long spat, to show the ducts of the digest ire diverticula leading into the stomach z 200 PLATE P la te 17. Key to the lettering* au. — a u r ic le . a .v .o . - atrio-ventricular opening. d .d . - digestive diverticula. d.p* — dorsal pericardium. e . p. — mantle eiifchelium. h. — h ea rt. h»m. — heart muscle. in t . — intenstine. ky. - kidney. i . g . - inner g ill. m. — m antle. P. - pericardium. p. a. - posterior adductor muscle. p .r . - posterior retractor muscle r . - rectum. r .p . - reno-pericardial duct. V. — v e n tr ic a l. F.g* - visceral ganglion* V.p* - ventral pericardium.

Figure 39. Diagrammatic reconstruction of the kidney of an 0.5 nuw long spat# The figure on the left is in frontal view, and the dotted line marks the outline of the lumen. Figure 39k* is a cross se ctio n at point A. Figure 39B. is a cross section at point B. x 900. Figure UO. Frontal section of the posterior dorsal region of an 0.5 mm. spat showing the heart, kidney and pericardium x 1000. Figure Lateral view of a reconstructed half kidney o f a 1 .0 Eta. long spat. Dotted line indi­ cates the reno-pericardial duct. Top of the diagram i s dorsal and th e l e f t i s anterior x IjOO. Figure 42# Frontal view of a reconstructed right half of a kidney in a spat 1.0 mm. in length xhOO. Figure k3• Sagittal section through the posterior dorsal region of a 1*0 mm. long spat, to show the h ea rt, kidney and pericardium x 600. Figure hit* Frontal section through the posterior dorsal region of an 0.35 mm. long spat, to ^iow the heart x 350. PLATE 17

A

FIG.39 FIG. 4 0

FIG.43

FIG.41 FIG.42

P.

FIG.44 Km l A q. .tl*v.lgfctvgliM fr a. - anas. a.a. - anterior adductor muscle, c.pg.- cerebro-pleural ganglion, f . - f o o t , i.g. - inner gill. 1. - ligament. m. - mantle. oes. - oesophagus. p.a. - posterior adductor muscle. p.r. - posterior retractor muscle. r. - rectum. u.p. - upper palp.

Figure k5* Braving of a whole amount of a 1.0 mm. spat from the right side x 100* PLATE 18

,o.e.s.

a.a.

m .

si.t.

FIG.45 E M s J f i. Key to the lettering* a . a . anterior adductor muscle. a .h . - anal hush. a .r . - anterior retractor muscle. fc.g. fcyssal gland. fc.gr. - fcyssal groove. e .g r . — ciliated groove. d .d . — digestive diverticula. f . - f o o t . g .s . gastric shield. g . - gonad. h . — h ea rt. i . g . - inner g ill. in t . • in te s t in e . k .s . - crystalline style sac. m. - m antle. m .c. — mucous c e l l s . QUO. - mouth* o es. - oesophagus. p . a. — posterior adduetor muscle. p .g . — pedal gangl ion. P*r. • posterior retractor muscle* p .c . pericardium. 8. — stomach. S t. mm s ta to c y s t. v .g . — Visceral ganglion.

Figure 46. Sagittal section through the approximate middle of a 1.0 mm* spat, to shot the relationship of the various organs at this stags x tOO. PLATE P la te 20 Graph showing the efficiency of the plates held at various angles as collectors of spat. The broken line represents the catch per square inch of t>rojected area, and the solid line represents the actual area exposed. The data are taken frost Table 6a and are the combined figures for glass and T ufnol. PLATE ANGLE SURFACE OF ANGLE

ro

CMCMCD O ^ I HONI 3dVnfcS d3d lYdS JO d3QKMHN t m x i i - Graph showing the nuniber of spat on k to sh sq u a re ground glass and Tufaol p i s t e s , hold at v a r io u s angles from the perpendicadhr through 360 degrees* The solid line is Tufnol, and the broken see ground glass* Bata from Table 6. PLATE 21 ANGLE SURFACE OF ANGLE 3 0 0 3 60 0 9 120 ISO 180 210 240 270 300

CVI CM 31VHd d3d IVdS 30 d3flWnN PLATE 22

FIG. 2 P la te 23 Figure 1* Photograjh of the Cross Houses Beach, M illp o rt, looking south-east across th e month of Karnes Bay. Kote the numerous rocks and stones and the attached littorlnes. The h ig hr eef shown in the upper right affords considerable protection from wave action in southerly gales.

Figure 2 . Photograph showing the plankton pump ap p aratu s at the shore station on Keppel Point. The intake pipe m am lag up the rocks from th e buoy nay be seem on the l e f t . The two § cubic metre measuring tanks are seen on the right, w ith th e plankton n e t in the o u te r one. PLATE 23

FIG. 2 m i & j i k * draph showing the distribution of spat from, th e spatfalls for the sowers of 1fl*6 and 19h7* at various tidal levels in Btllaeh B a y * th e s o li d line is the Septeniber t$M* distributism , and the broken line that of October 19h7* B a ta fro® Tables 7A, IB, ?C. L I F A D M U T DA E V O AB T E FE IN L E V LE E D I T PLATE 24 JO d3gwnN JO (VI d3d IVdS lOOJ 3«vn0s lOOJ

oos ZlS££~2Se Graph showing the length~frequeacy distributions of samples of spat from various tidal levels in Bslloeh Bay, Septeoiber The sta tio n numbers are merited on e&eh curve, which has its own hase lin e, so the curves are comparative hut frequences must he calculated hy estimation and subtraction* Bata from Table 26a • FREQUENCY 2 0 0 3 IOO 0 5 2

150 00 0 5 OO 4.5 203 h t g n e l in mm 353 . 503 LT 25 PLATE Gr&pk growing sieaa im x g th s o f s a b l e s o f spat tr* m vt irioue 1 iclal le rols at Bal ioeh Bajr* Septe&fcer 19^*6* Eats f rom TaBle &* PLATE 26

*o

(VJ •TIDE LEVEL •TIDE IN FEET ABOVE DATUM

v IO C\J — m NI H10N3H NV31M EMS&JZ* G raph shoeing the parcel age mortality of sp a t f r o a B a llo c h Bay, at ^aricAis lisaae, from Septeu&er t9ty6 t© June 1947 * Bata from Table® H , % , © ?D« PLATE 27

Ui z

Lu

•O •O (M Ainviyon 39VlN3Dd3d Plate 28. Graph showing the rate of removal of a coloured suspension. The ordinate is on a sliding scale, in order to accommodate sufficient nu 2s&er of curves, and represents the natural logarithm of the ratio of the ” speaker *1 reading at eny given time, to the original wspeicker” reading. Data are from Experiments 3 to ik. inclusive, Appendix 1* ,OV)*S P la te 29. Graph showing the pate of removal of a coloured suspension# The ordinate Is on a e lid in g seal** In order to accommodate sufficient curves* and represents the natural logarithm of the xatle o f the *spekker,! reading at car given tiiaef to th e original ” speaker” reading# The data are taken from Experiments 15 to 38 Inclusive* Appendix 2# PLATE 29

ttlO L z _ l 32

36 35

36 TIME IN HOURS P la ta 29k. Graph showing the rates of filtration in Experiments 2 d to 31, In which the suspension medium was colloidal graphite# The animal® in Experiments 3 $ and 31 had heen fed for three hour® previous to the experiment with a concentrated rouge eolation* Be script ion of the experiment, page 92 . PLATE 29A

c c | q l z 2 8

2 9

3 0

O 2 3 TIME IN HOURS P la t e 30 * Graph showing the rate of filtration as shown hy the relative changes in concentration (m ^ |) of a coloured suspension with time* The lower line of long dashes shows the plotted logarithmic ratios* and the line of short dashes shows a line fitted hy the method of Least Squares* The upper line of long dashes is the plotted logarithmic ratios of the control experiment which shows the rate of settling of the suspension. Late from Experiment Ho. 3 5 * Appendix I* PLATE 30

180

120 TIME TIME IN MINUTES . Diagram showing the apparatus used to obtain kymograph recordings of the shell movements*

te g s M * A - Anchor block# B - Sealing wax* 0 - Animal. D - $ire connecting animal to vertical lever* EPS - Vertical lever swung at F. 0 - Block supporting Hlng^F* IJK - Unit lever combination swung at g* M - sand* H - water level. P - w all of aquarium . PLATE Jr’lcJ.laG 3^*

Tracing 1* Shell Movements !*.« 7- k&* k hours and 50 mine* recording shown on the tracing* Open 100$ of the period* Mean degree of open-nees 73$* A certain rhythm apparent* Temperature 16.6 - 18.0 degrees 0*

i Tracing 2* Shell Movements k /5 * 7. M>* 2 hours and 30 mine* recording shown on the tracing* Open 100$ of the period* Ho definite rhythm apparent. Temperature 19.0 - 20*8 degrees 0*

i iI I Tracing 3« Shell Movements 12/13. 7* U&* k hours recording | shown on the tracing. Open 90$ of the period* Mean degree of open-ness 90$* Rhythm not ; apparent* Temperature 19*3 degrees €• I I - E m ■ ■ ■ ■ ■ ■ ■ ■ T ra cin g 1* Shell Movements 5* 7* 4&* 3 hours recording shown on the tra cin g . Open 100$ o f the period* Degree of open-ness 90$* Closure at 4-mta*te intervals. Some evidence of rhythm. Temperature 18*5 - 20.4 degrees C.

JjfiSiSfiL2* S h ell Movements 5* 7* 46* 3 hours recording shown on the tracing. Open 100$ of the period. Mean degree of open-ness 75$. Mo definite rhythm. Temperature 1 6 .6 - 18.0 degrees C.

Tracing 3* Shell Movements 12. 7* 46. 2 hours and 25 mins. recording shown on the tra cin g . Open 100$ ©f the period. Mean degree of open-ness 80$. Definite rhythm* Alternate activity as shown and inactivity at hourly intervals. Temperature 18.0 degrees C.

Tracing 4 . S h ell Movements 4/5« 7. 46. 2 hours and 30 mine. recording shown on the tracing. Closed shells for several short intervals. Rhythm evident. Temperature 19.0 - 22.0 degrees 6. PLATE 33 P la te 34

Tracing 1. S h ell Movements 10. 7* 46. 3 hours and 25 mine. rebording shown on the tracing. Open 100$ of the period. Rhythm not definite. Temperature 19*5 - 21.5 degrees C.

Tracing 2. S h ell Movements 10. 7. 46* 3 hours and 25 mine. recording shown on the tracing. Open 100$ of the period. Mean degree of open-ness 85$* Some indication of a rhythm. Temperature 20.3 - 21.3 degrees C*

Tracing 3. Digging Movements, soft sand. Muniber of consecutive sequences is 1 8 , and th^ b * e mean V*t£fc

T racin g 2. Not significant in relation to spawning* Ordinary shell movements.

Tracing 3 . Spawning Movements 8 , 7* 47* began spawning 14.20 hours. Harnessed to the kymograph after several difficulties by 14*38 and restarted spawning at 14*40 hours. There was considerable pedal activity but no associated shell movement as can he seen from the tracing. Shell closure by stimulation was carried out at 14*44 hours, 8 minutes of recording is shown on th e tra cin g . Temperature 18 degrees C.

T racing Spawning Movements 12. 7- 47* Female spawned between 2 2 .1 0 and 22.25 hour 8 . One hour and 20 minutes i s shown on th e tra c in g , 0 .1 n . 0.8 min. Temperature 16.1 degrees C,

T racing 5 Spawning Movement 9 . 7- 47* Female began w r spawning vigorously at 18.52 hours. First peak thereafter caused by a stimulated shell closure. One hour of recording is shown on the tra cin g . Temperature 16*0 degrees C, PLATE 35 P la te 56» Figure 1* Phot omierograph of a gonad section of a hermajjhrodite, October 21 st, 1 9kl* Residual ova are seen among the follicle cells in the female section (left)* Heidenhain* 7 a. x 5W*

Figure 2* Photomicrograph of developing female, August 20th, A considerable number of residual ova are le ft 2 The ovocytes and follicle cells ere seen against the alveoli walls* Heidenhdiru 7 u. x 5U0.

Figure 3* Photomicrograph of a gonad section of a ripe female, June 23rd, 19M>* The large ova are seen, some free in the lumen and some still attached to the f o llic le wall* Heidenhain* ? u . x 1200*

Figure h* Photomicrograph of a gonad section o f a ripe female, June 23rd, 19M>* Young ovocytes are seen on the follicle vails* Heidenhain* 7 u. x 5h0* PLATE 36

o a / p # ®V t^° "^Vp. -V^"| * P '££*% ;!* .• V •’ fc. iS ^ V ■ '/ ’ 6 < L;P i •• « » *T 4 ^ « * ;0 # ^ O r .. . 3*| §. * ;... i

FIG. I FIG. 2

FIG. 3 FIG. 4 Figure 1* Photomicrograph of a gonad section of a spawned out female, July 26th , 1947* A few residual ova are seen, and some of the follicle walls appear to he broken down* Heidenhain. ?u, x 540*

Figure 2* Photomicrograph of a gonad section of a spawned out female, July 26th, 1947* A few residual ova may he seen. Heidenhain* 7 u* x 1200*

Figure 3* Photomicrograph of a recuperating female, September 21st, 1947* The f o llic le e e lla and a few young ovocytes are seen* The residual ova are still present* Heidenhain* 7 u* x 1200*

Figure 4* 'Photomicrograph of a gonad section of a recuperating female, November 23rd, 1946* The lumens are filled with follicle cells and numerous ovogonia are seen on the follicle walls. Several residual ova are seen* Heidenhain. 7 u* x 540* PLATE P la te 38* Figure 1. Photomicrograph of a gonad section of a male, Oct otoer 1947* Shows the columnar arrangement of the sex c e lls , with the primary gonia along the f o llic le w all, and the sperms and spermatids in the lumen* Heidenhain* 7 u* x 540*

Figure 2* Photomicrograph of a gonad section of recovering male showing a typ ical "pattern” formation, October 21st, 1^47* The sex c e lls appear to he arranged around the periphery of the follicle cells* Heidenhain. 7 u. x 300*

Figure 3* Photomicrograph of a gonad section of a male, June 23rd, 1946* The lumina of the f o llic le s are nearly f u ll of sperms. A few developing gonia may he seen along the outside edge of the f o llic le . Heidenhain. 7 u. x 540.

Figure 4 Photomicrograph of a gonad section of a male, May 25th, 1946* The spermatogonia and spermatocytes are scattered loosely throughout the lumina of the fo llic le s * A small nucleus of spermatids and sperms may he seen in the upper right. Heidenhain* 7 u. x 540* PLATE 38

FIG. 3 FIG. 4 B l a t e 39. Figure 1* Photomicrograph of gonad section of spawned out and recuperating male, September 18th, 1946. Note the follicle cells andthe thin walls of the tubules. Heidenhain. 7 u. thick x 1200.

Figure 2. Photomicrograph of gonad section of a male almost completely spawned out, August l e t , 1947. The few sperms are lying in the centre of the tubule. Heidenhain. 7 u. x 2160.

Figure 3. Photon&crograph of a gonad section of a spawned out male, August 1 st, 1947* A few sperms still lie along the walls of the follicle. Heidenhain 7 u. x 1200.

Figure 4* Photomicrograph of a gonad section of a spawned out male, August 1 s t, 1947. Note the strands of muscle outside the follicle wall on the right. Heidenhain. 7 w. x 1200. PLATE 39

FIG. I FIG. 2

FIG. 4 FIG. 3 P la t e hO* A series of photographs of spat of various sizes from Balloch Bay. The sizes are given below in the same relative positions* The left hand series do not show a winter ring, as it has not yet heen formed, hut will he in the position marked R1* These were taken September 3rd, 19U6* The right hand series were taken June 2nd, t9U7> and the winter rings (Rt) are shown* Note the prodissoconch (Prod*) on the small spat in the left hand comer.

Sizes of spat in mm. 1*63 1.75 3.18 3.70 1.36 1.75 PLATE 40 P la te h i. Photographs of spat of the brood year 192*6 from Balloch Bay, the sizes of which are given below in the same relative position as they appear in the plate. The le f t hand pair, taken June 2nd 192+7, show the winter ring (R1). R2 shows the position of the second ring which, of course, has not yet been formed. The right hand pair were taken September 3rd 19M>, and the winter ring (R1) is S till in the process of being formed.

Sizes of spat in am. 6.82 5*52 5.2*6 2+.35 PLATE 41 P la te hZ. Graph showing a length-frequency distribution «T a Jtm e, 19^6 random sample from the Crow Houses Beach Bata taken from Table 1TM* PLATE

•o

ro .

O* m m (Vi

in

length

(VI ZMiSwSkl# Graph showing the length increscent gained by the rarious age (Ring nuafcer) group*, marked and planted an a beach on Horth Cuabrae, for the period Septeafcer 17th, te October 20th» 19h7* Bata taken from Table Id* PLATE n u m b e r

ring

i/i ^

«o RING RING NUMBER

m

n n Nl H19N31 P la te h i. Graph showing the length-f re quency distribution of a ll the ring length measurements for the October random sample of adults from the Cross Houses Beach* The data is taken from the in itia l ring measurements and this information is not given as such in any of the Tables* 80 PLATE Graph shoving the mean monthly increment of a ll sixes for the period April to 3eptss£»er» 1W7* The data ie taken from Table 21* The broken line is the mean weekly temperature over the period* 14.0 -yin l NWbN A1H1NO !N3W3bONI Nl m EPRTR #C. TEMPERATURE CM VH NV3IAJ o

AUGUST SCPT£M6CR PLATE za&i&je* Graph showing the heikht-length (unbroken line) and the thickness*-!ength line) ratios of warioaa sizes of adults from the Cross Bosses Beach 19M>+ The data is taken from Table 23* and the lin es are drawn as theybest fit by inspection only* The dote represent the plotted data* PLATE

K>

< \J LENGTH LENGTH IN MM.

<0 CM K) CM WIN Nl SS3N>IDIH1 QNV 1H9I3H P late SO. Dlagranmetle representat ion of the digging Movements ae described In th e text* *XX# and TYTf are vertleal and horizontal lines of reference* PLATE 50