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BRITISH MUSEUM (NATURAL HISTORY) Economic Series No. 10

MARINE BORING ANIMALS

INJURIOUS TO SUBMERGED STRUCTURES

BY if W. T. CALMAN, I J. So.

Assistant in the Department op Zoology

WITH 21 TEXT-FIGURES.

LONDON

PRINTED BY ORDER OE THE TRUSTEES OE THE BRITISH MUSEUM B SOLD AT The British Musedm (Natural History), Cromwell Road, S.W. 7,

and by B. Quaritch, Ltd., 11, Grafton Street, New Bond Street, W. 1, and Dulau & Co., Ltd., 37, Soho Square, W. 1. 1919 All rights reserved.

Original from and digitized by National University of Singapore Libraries \ CONTENTS.

TAGE Preface 3

Introduction 5

Animals Boring in Timber 7 The Shipworms 7 Other Wood-Boring Mollusca 17 The Gribble (Limnoria lignorum) 17

Other Wood-Boring Crustacea • 20

General Remarks on Timber Pests 22

Animals Boring in Rock 24 Rock-Boring Mollusca 24 Other Rock-Boring Animals 27

General Remarks on Rock-Boring Animals. . . 30

List of Books and Papers referred to ... 32

Index 35

Original from and digitized by National University of Singapore Libraries PREFACE.

The existence of an animal known as the " Shipworm " is a fact familiar to naturalists and marine engineers, many of whom have been confronted by the serious damage it sometimes causes to the timbers of wfcybden ships or of harbour-works. The Zoological position of this animal is not universally understood. Those who are better informed may recognise that it is not really a worm, and that on the contrary it is one of the Bivalve Mollusca, and therefore, a relation of oysters, mussels and cockles; but even among this class the general outlines of its life-history are often very imperfectly appreciated, nor is it always recognised that the term " shipworm " includes a certain number of distinct species or even ^genera of molluscs. Some of these will only live in salt water, while others show a considerable tolerance for water which is brackish or even fresh; and the accurate determination of the species may accordingly be a matter of practical importance. In considering methods by which submerged timber can be protected, it is further essential to know something of the life-history, and thus to be in a position to recommend measures for preventing the entrance of the mollusc into the wood. The Shipworm is, however, not the only boring animal whose attacks have to be feared. Other species of Mollusca and several species of Crustacea may be very destructive to wood; while boring animals, of these or other classes, may also do serious damage to rocks, and thus affect marine constructions or even play their part in coast-erosion. The Trustees of the British Museum have accordingly thought it advisable to sanction the preparation of a small exhibit illustrating the Natural History of boring marine animals and the destructive effect they may have on timber and rocks. The exhibit has already been installed in the Central Hall of the Museum, and the following general account, prepared by Dr. W. T. Caiman, has been written as an aid to the understanding of the exhibit, and as a summary of the facts in the Natural b 2 Original from and digitized by National University of Singapore Libraries 4 Preface.

History of the animals concerned which, it is hoped, may be found useful both to Zoologists and to marine engineers who are interested in the practical application of the facts recorded. The preparation of the exhibit and of this guide-book was undertaken by Dr. Caiman in connexion with work he has been doing as scientific adviser to a Committee of the Institution of Civil Engineers engaged in the production of a Report dealing with the economic aspects of the subject. The thanks of the Trustees are due specially to this Institution for assistance which has been given to Dr. Caiman, by supplying specimens and in other ways.

SIDNEY E. HARMER, Keeper of Zoology.

* British Museum (Natural History), Cbomwell Road, London, S.W. 7. June 2, 1919.

Original from and digitized by National University of Singapore Libraries INTRODUCTION.

A great many of the animal inhabitants of the sea burrow in the sand, mud, or clay of the sea-bottom to obtain concealment or

protection _ from their enemies; a certain number, belonging to very diverse groups of the animal kingdom, go further than this and are able to excavate shelters for themselves in solid substances such as wood and stone. These boring animals are of special interest from several points of view. The modifications of structure associated with their peculiar habitat, the convergence of character between species of widely different affinities, and the problems, still largely unsolved, relating to their methods of boring, deserve the attention of the zoologist. The rock-boring species have afforded to geologists evidence of change in the relative levels of land and sea, and are recognised as important agents in the erosion of our coasts and as influencing the formation of coral islands. On the other hand, the practical importance of some of the timber-boring species is notorious. The dreaded Shipworm— " calamitas navium " as Linnaeus called it—has been an enemy of seafaring men since ships first sailed the seas. It attacked the triremes of Athens and the galleys of Venice, it rotted the timbers of Drake's " Golden Hind," * and it is causing anxiety in the present-day revival of wooden shipbuilding: in the dykes of Holland it has more than once threatened disaster to a nation, and in many parts of the world it still defies all the resources of the harbour engineer.

* " Quales [sc. Teredines] etiam inclytus ille Franciscus Drakus, alter quasi Maris Neptunus, in nave sua orbivaga (carie jam pene spongiosa) domum reduxit." Thomas liloffett, Inseotorum Theatrum, 1634, p. 250. Moffett, who was born in 1553, knew Drake and may have seen what he describes. The Museum possesses a piece of oak planking showing Teredo borings, taken from the wreck of a sixteenth century ship, found some years ago at Woolwich. It has been suggested, but not definitely proved, that this was the wreck of the "Golden Hind."

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The rock-boring species are less often accused of being destructive agents, but it is stated that, in some cases, they have endangered the stability of structures built of stone. Finally, the materials used in the casing of submarine telegraph cables are liable to attack by certain species which normally live in wood, and many failures of insulation are due to this cause. In the following pages some account is given of the more important timber-boring and rock-boring animals that attack submerged structures. No attempt has been made to discuss the practical problems connected with the preservation of timber and the like, for which reference must be made to technical and engineering publications, and, in particular, to a~ forthcoming report by a Committee of the Institution, of Civil Engineers which deals with these subjects as they affect harbour engineering.

Original from and digitized by National University of Singapore Libraries MARINE BORING ANIMALS.

ANIMALS BORING IN TIMBER.

' Eungi and Insects, the two groups of organisms that cause most damage to timber on land, are almost absent from the sea, but the marine Crustacea, which in many other respects take the place of terrestrial insects, include several wood-boring species that are common and very destructive. Even more important, however, are the Mollusca, which comprise, besides the well- known shipworms, several other species of similar habits which may occasionally do serious damage.

THE SHIPWORMS (TEBEDINIDAE).

Although the shipworm is mentioned by some of the ancient Greek and Roman writers and was discussed by naturalists of the seventeenth century, its scientific study can hardly be said to have begun before the eighteenth century. About 1730, great damage was caused to the timber-work of the dykes in Holland, and several Dutch naturalists were led to study the pest. Among these was Godfrey Sellius (1733),* whose learned treatise may still be consulted with advantage. Since that time many naturalists in various parts of the world have given attention to the subject and much has been written on the structure, habits and life-history of the shipworms. Among many others, reference may be made to the important memoirs by Quatrefages- (1849); to the series of reports issued by a Commission of the Royal Academy of Science in Amsterdam (1860-1869); to Hatschek's (1880) account of the early develop¬ ment; and to Sigerfoos' (1908) elaborate monograph on the structure and life-history of a species found on the American coast. More than thirty species have been described and they have been assigned to some five or six genera besides the typical

* The names of authors followed by a date in parentheses refer to the list of hooks and papers on p. 32.

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genus Teredo, but the classification is not in a satisfactory state, and a systematic revision of the whole family Teredinidae is greatly needed. The shipworms are not " worms" even in the somewhat indefinite sense in which that term is employed in systematic Zoology. They are Mollusca belonging to the Class Pelecypoda (or Lamellibranchia) which includes those forms that have bivalved shells, such as oysters, mussels and the like. They differ greatly in appearance from the more familiar types of that Class, however, for the two valves of the shell are reduced to a pair of small plates (Tig. 1, s.) at one end of the long, soft, worm-like body. This is the front end, and when the animal is exposed Jiy splitting the wood in which it is living, the valves are seen to lie at the inner end of the burrow. They are, in fact, as will be shown later, the organs by which excavation of the wood is effected. At its other end the body narrows towards a small opening oh the surface of the wood, from which, during life, a pair of fine extensible tubes,

Pig. 1.—A Shipwobm, Teredo navalis. c.8. Exlialent siphon. /. Foot. i.s. Inhalent siphon. One of the pallets, s. One valve of the shell.

of unequal length, are protruded. These tubes or " siphons" (Fig. 1, e.s., i.s.) serve for the entrance and exit of the water required for respiration. They lead into two passages running the whole length of the body and separated by a partition formed by the gills. The gills have a complicated lattice-like structure and are covered with fine vibratile hairs or "cilia," by the movements of which a current is kept constantly flowing from one passage to the other. At the base of the siphons are a pair of shelly plates known as the "pallets" (Fig. 1, p.), which serve to block the entrance to the burrow when the siphons are withdrawn. The pallets differ much in shape and afford the readiest means of distinguishing some of the species. In the genus Teredo they are paddle-shaped (Fig. 2, c), with a slender handle embedded in the substance of the body. In the allied genus Xylotryd they are made up of a series of segments with a long stalk, and may look like a pair of quill-feathers sticking out from the surface of the wood.

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The valves of the shell (Fig. 2, a, b) have a complicated form and differ in many ways from those of the more familiar bivalves. On the front edge (next the inner end of the burrow) the outline is interrupted by a deep right-angled notch, looking as if a part of the shell had been broken away. Parallel with the edges of this notch the outer surface is engraved with a series of fine ridges and grooves. Under the microscope the ridges are seen to be rows of fine sharp-pointed teeth, resembling those of a file or rasp. These teeth, brought into contact with the surrounding wood by the movements of the valves, are the instruments by which the wood is rasped away in excavating the burrow. Throughout the

Fig. 2.—-Teredo norvegica. A. Outer surface of right valve. The notched front edge is to the right and the two sets of line ridges are seen parallel to the edges of the notch. B. Inner surface of left valve showing the dorsal and ventral knobs and the inner blade. C. One of the pallets. (Enlarged.)

life of the animal, as the shell grows, new rows of teeth are continually being added along the edges of the notch, and the latest formed and least worn teeth are in the most favourable position for acting on the end of the burrow. Owing to the notches in the front margins, a, large gap is left between the valves in front, and this gap is occupied by a fleshy plug, known as the " foot," the flat surface of which acts as a sucker, adhering now to one part and now to another of the inside of the burrow.

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In most of the bivalve Mollusca the valves of the shell are united along the dorsal side by a hinge, usually provided with interlocking teeth, and with an elastic ligament which acts as a spring, so that the valves gape when the tension of the muscles is relaxed. These muscles which draw the valves together are known as the adductors, and are normally two in number. In the shipworms the connexion of the valves is very different. The ligament is absent or reduced to the merest vestige, and there is no other provision for separating the valves. The hinge is repre¬ sented by a prominent knob on each valve which works against its fellow (Fig. 2, b). On the ventral edge is another knob which forms a second point of contact between the valves. "Of the two adductor muscles the posterior is very large and is attached on each side to the inner surface of a projecting posterior lobe of the shell known as the auricle. The anterior adductor is very small and runs between the edges of the two valves just in front of the dorsal knobs. It is evident from the arrangements thus briefly described that the movements of the valves must be very different from the simple opening and shutting of a mussel, for instance. The two valves always remain in contact by the dorsal and ventral knobs while gaping widely in front and behind. It appears, in fact, that the two adductor muscles, instead of contracting simultaneously, as in ordinary bivalves, do so alternately, drawing together now the front and now hinder the edges of the valves. In this way there is produced a rocking movement of the valves on the pivots formed by the dorsal and ventral knobs, and this movement causes tire ridges on the outer surface to rasp against the wood. On the inner surface of each valve a narrow curved blade (Fig. 2, b) is attached close to the dorsal knob, and its free end is deeply buried in the soft tissues of the body. Certain muscles of the foot are inserted on these blades, and it is not unlikely that their action may produce a twisting movement of the whole shell to aid in the process of boring. The sucker-like foot changes its place of attachment from time to time so that the wood is worn away equally on all sides, and the circular form of the burrow is preserved. The method by which the shipworms excavate their burrows has been the subject of much discussion, but it is now generally agreed that the shell is the boring organ. This is placed almost beyond doubt by the fact, which seems to be well attested, that, under favourable conditions, a rasping sound may be heard

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when ear the is applied to a, piece of timber containing living shipworms.* Throughout the greater part of its length the burrow is lined with a layer of shelly material. Towards the inner end this layer is no more than a mere film, but near the opening it may be considerably thicker, and, where the superficial layers of the wood have been removed by decay, the shelly tubes may project for some distance (Fig. 7). In some species the lining of the burrows has successive rings projecting inwards so as to divide the tube partially into a series of chambers (Fig. 5). Under certain circum¬ stances, possibly when the animal has reached the limit of its growth, it jjiay withdraw a little from the end of the burrow and shut itself off by a dome-shaped septum continuous with the shelly lining. In this way the animal becomes completely enclosed with shell, and is nowhere in contact with the wood. As a rule the burrows enter the wood at right angles to the direction of the grain, but soon turn to run with the grain, generally upwards in the case of a pile standing vertically. In timber that has been heavily attacked by shipworms, the burrows may be so closely set that only thin layers of wood separate them. Even tinder these circumstances, however, the burrows never break into one another. In one of the specimens exhibited (Fig. 3), a shipworm on the point of breaking into a neighbouring burrow is seen to have withdrawn for about two inches and to have started afresh in a direction at right angles to that in which it had been working. The mouth of the shipworm is a small opening situated just above the foot. As in most bivalve molluscs it is flanked by two pairs of ciliated flaps (the labial palps) which serve to draw into it the minute organic particles and floating organisms (plankton) which are brought in with the respiratory current. At the same time the ciliary current sweeps into the mouth a good deal of the fine "-sawdust" produced by the rasping of the shell on the wood, and the food-canal is largely filled with this material. There has been a great deal of discussion as to whether the shipworm really feeds on the wood through which it burrows, or whether it depends entirely on the plankton for. its nourishment, as so many bivalved molluscs do. The finding of wood fibre in the digestive tract is

* " Bodunt dentibus, perforantque robora, vel sono teste."—Moffett, 1634, p. 250. " They gnaw with their teeth and pierce into Okes, as you may know by the noise." Topsell's translation, 1658.

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not of itself decisive, since some of the rock-boring molluscs swallow considerable quantities of the mud produced by their boring. It has been pointed out that certain peculiarities in the structure of the food-canal of the shipworms may be interpreted as adaptations to a bulky and relatively innutritious diet. There is a large side-branch or caecum, opening into the stomach, which is found on dissection to be completely filled with particles of wood. In some species, but not in all, this caecum is provided with a spirally coiled internal fold. This fold, like the " typhlosole " of

bysstis thread

Fig. 3.—Burrows of Fig. 4.—Stages in Development Shipworms. of the shipworm.

A wire passed into one of the burrows A. Tree-swimming stage. B. Creeping stage showing a change of direction on ap¬ after settling on surface of wood. C. Stage proaching a neighbouring burrow as shortly after beginning to burrow. (A. Teredo, described in the text. after Quatrefages. B and C. Xylotrya, after Sigerfoos. All much enlarged.)

the earthworm, greatly increases the digestive and absorptive surface, and it has been suggested that, whether the fold be absent or present, the caecum is specially concerned with the digestion of woody-fibre. In any case it is certain that the plankton brought in by the respiratory current furnishes at least a part of the food supply, and must provide the whole in the ease of individuals that have ceased to grow and have become shut off from the wood by" a

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shelly septum in the manner described above. It would seem probable, therefore, that the richness or poverty of the plankton in different localities must be taken into account as one of the factors determining the distribution of the shipworms. Some species of Teredinidas are stated to be hermaphrodite, both sexes being united in each individual, but in others the sexes are separate. The eggs and sperm are usually discharged with the outgoing current from the gills and fertilisation takes place while the eggs are floating freely in the sea. In some species, however, as in the common T. navalis, the eggs remain in the gill-chambers of the female and are fertilised by sperm drawn in with th£ entering current. The early stages of development are then passed through within the gill-chambers. In either case the egg develops in a few hours into a minute larva (Tig. 4, a) which swims freely in the sea by means of a circlet of cilia. Very soon the bivalve shell is developed and it has at first a simple symmetrical form, like a microscopic swimming cockle. The valves enclose the whole body of the animal, not, as in the adult, only an inconsiderable part of it. How long the larva continues to swim freely in the water is not definitely known, estimates that have been made varying from four days to a month. It is during this period alone that the shipworm possesses the power of locomotion and is able to infect timber previously untouched. The next stage known (Tig. 4, b) is that in which the larva has ceased to swim and has settled on the surface of the wood. It has lost its circlet of cilia but is able to crawl about by means of the large muscular foot, which is a tongue-shaped organ protruded far beyond the shell and very differerft from the small sucker-like foot of the adult. As in many other bivalve molluscs, there is at this stage a special gland in the foot which secretes a sticky thread known as the byssus." When the young animal finds a suitable place to begin boring, it attaches itself by means of the byssus thread and starts to scrape away the fibres of the wood with the edges of its valves. According to one observer it covers itself with a protective case formed of particles of wood and other substances stuck together. Under this covering it works rapidly and soon disappears beneath the surface of the wood. At this stage (Fig. 4, c) the animal is still very small—less than T^-th of an inch in the species in which it has been most fully studied—and although the opening of the burrow may be somewhat enlarged later, it remains little more than a pinhole even when the shipworm is full-grown. These minute openings may be the only

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external evidence that a piece of timber has been attacked, although the interior of the wood is riddled with burrows. The breeding season, at least in temperate climates, is in the summer months. Teredo navalis, on the Dutch coast, was found to carry eggs in June and July, and larvae were found settling on wood from July to September. Probably, in most cases, only a few individuals survive the winter. The rate of growth and the size reached by the adult vary according to the species and probably also according to the conditions of food-supply and temperature. Sigerfoos (1908) gives the following figures for the rate of growth of Xylotrya gouldii at Beaufort, North Carolina :— * Leftgth in millimetres Just attached to wood 0*25

12 days after attachment 3 ■ 0

16 „ „ „ 6-0

20 „ „ 11-0 30 „ „ „ ..... '63-0 36 „ „ 100-0'

At the same place specimens of Teredo dilatata four feet long were estimated by Sigerfoos to he " little, if any, over a year old." Orton, at Plymouth, found that Teredo navalis excavated burrows 280 mm. (11 inches) long in 31 weeks. Full-grown specimens of T. navalis may be from 12 to 16 inches in length and the burrow is about 1th of an inch in diameter. In Australia an allied species is recorded as growing to, and possibly exceeding, 5 feet 10 inches in length, the burrow being from | to 1 inch in diameter.

Shipworms may attack timber at least as high as midway between tidemarks. The greatest depth at which they may occur does not appear to have been satisfactorily determined. The related genus Xylophaga is stated to have been found in a telegraph cable at the great depth of 1,500 fathoms. It has been that timber observed placed in muddy water or in water heavily contaminated .with sewage or factory waste is less, likely to be attacked than when placed in clear and fairly pure water. With regard to the salinity of the water, the various 'species differ in their requirements. Teredo navalis appears to be intolerant of brackish water. The great outbreaks of this species in Holland in 1730-32, 1770, 1827, and 1858-59 are said to have been associated with reduced rainfall, leading to unusually high

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salinity in the Zuyder Zee and coastal waters. More recently, outbreaks of T. cliegensis in the inner parts of San Francisco Bay have followed years in which the outflow of the Sacramento and San Joaquin rivers was unusually low (Barrows, 1917). Certain species

TEREDO NAVALIS. Valves of shell and pallets.

TEREDO NORVEGICA. Valves of shell, pallets, and lining of burrow.

TEREDO MEGOTARA. Valves of shell, pallets, and lining of burrow.

Pig. 5.—Shells, etc., op Three Common British Species op Teredo. About natural size.

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found in tropical countries, however, are stated to live in perfectly fresh water.

Specimens of T. navalis were found by Orton (1914) to be alive a fortnight after the wood containing them had been taken from the sea, and he adds, " Thus these animals would be able to live easily during the period for which most vessels would he in dry dock for scraping and painting." When the shipworm has penetrated into the wood it is probably secure from the attacks of most predatory animals. A species of annelid worm, Nereilepas fucata, has been stated to prey upon Teraclo navalis, entering the 'burrows and devouring the occupants piecemeal. Some authorities, however, doubt the accuracy of this statement, and, at all events, there is no evidence that the attacks of the annelid are efficient in checking the depredations of the shipworm. As already stated there is no general agreement as to the number of species to be recognised within the family Teredinidae or as to the limits of the genera in which they are to be classified. Of the typical genus Teredo, three of the commoner British species are exhibited (Fig. 5). T. navalis is the species doing damage on the Dutch coast, in the estuary of the Thames and elsewhere on the East coast of England. It is distinguished by the form of the pallets, which are notched at the end. T. norvecjica, a somewhat larger species, with simple racquet-shaped pallets, is found on many parts of the British coasts and ranges north to within the Arctic circle in Norway. According to recent accounts both T. navalis and T. norvegica occur in Australia and the latter also in New Zealand. Another species, T. megotara, distinguished by the large recurved posterior lobe of the shell (auricle), is not unfre- quently found in British waters, but chiefly, it is said, in floating timber. The segmented feather-like pallets of the genus Xylotrya have been mentioned above. The species of this genus are especially characteristic of the warmer seas although several have been found on the British coasts. Several of the other genera which have been distinguished under the names Nausitora, Calobates, etc., are of doubtful validity and some authorities even go so far as to include all the known shipworms in the single genus Teredo.

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OTHER WOOD-BORING MOLLUSCA.

Apart from the true shipworms of the family Teredinidae, the only wood-boring Mollusca are certain species- of the related family Pholadidae. Most of the Plioladidae are rock-boring animals and will be discussed later. Some species of the typical genus Pholas have occasionally been found in timber and this is the normal habitat of the species of the genera Martesia and Xylophaga. Martesia striata is a tropical American species sometimes found in the timbers of ships coming from the West Indies. Xylophaga clorsalis occurs or in fixed floating timber on the British coasts. It as is of interest forming in some respects a link between the families Tei^dinidae and Pholadidae. The valves of the shell closely resemble those of Teredo but the body is comparatively short (the burrows do not exceed 11- inches in depth), there are no pallets, and the burrow is not lined with shell. A pair of small accessory plates lie between the valves of the shell on the dorsal surface of the body. Xylophaga has been reported as doing serious damage to the dock gates at Ardrossan on the Firth of Clyde. Species of Xylophaga have repeatedly been recorded as boring in the insulating material used for covering submarine telegraph cables. Cable engineers frequently refer to faults in cables caused by " Teredo," but 110 special Teredo has hitherto been identified and it seems probable that Xylophaga has been mistaken for the true shipworm.

THE GRIBBLE (LIMNOBIA LIGNOBUM).

Next in importance to the shipworms as a destroyer of sub¬ marine timber is the little Crustacean known as the Gribble. It belongs to the Order Isopoda, which includes the common Wood- lice of gardens as well as a host of marine species of very varied habits. Attention was first drawn to the Gribble in this country by Robert Stevenson, the famous lighthouse engineer, who found it destroying the timber used in the erection of the Bell Rock lighthouse, off the east coast of Scotland, in the early years of last century. The Museum possesses specimens which were sent by him in 1814 to W. E. Dr. Leach, by whom they were described under the name Limnoria terebrans. Still earlier, however, the animal had been found by a Norwegian zoologist, TI. Rathke, who named it Cymothoa lignorum, and, according to the rules of

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zoological nomenclature, the earlier specific name must be employed. Limnoria (Fig. 6) is not unlike a miniature woodlouse in appear¬ ance. It measures from J-th to Jrth of an inch in length and has a semi-cylindrical body divided into segments, 'with a small head and a broad tail-plate. The head bears a pair of eyes, two pairs of short antennae, and a strong pair of mandibles (besides other mouth-parts) which are used in gnawing the wood to form the burrow. There are seven pairs of short legs ending in sharp curved claws with which the animal clings to the wood. Under the tail-plate are five pairs of appendages, each with two broad membranous plates which act as gills. During life these gills keep up a constant fanning movement causing a current which serves to renew the water needed for respiration. They Fig. 6 —Limnoria ar0 a^g0 ug0(j ag pa(jt"pes jn swimming when the ngnorum. L Enlarged (after Sars). G"ribble leaves its burrow. The last pair of appendages (uropods) are small and hooked and are placed at the sides qf the tail-plate. e The burrows are about ^th of an inch wide and of the same diameter throughout. They usually run obliquely to the surface of the wood, and although they may be 1\ to 2 inches long the average depth of penetration is not, as a rule, more than about half an inch (Fig. 8). The fact that the burrows are of uniform diameter indicates that the animal begins new ones as it increases in size, and as they break into each other in all directions, the superficial layer of wood rapidly becomes reduced to a spongy mass which is easily removed by the action of the waves. In this way the deeper layers are laid open to attack and in course of time the timber may be entirely destroyed (Fig. 7). It is very ljkely that a limit is set to the depth of the burrows by the difficulty of respiration. As already stated, the necessary current of water is kept up by the fanning movement of the gill-plates themselves, and it may easily be supposed that this movement is insufficient to maintain a regular circulation at the inner end of the burrow beyond a certain depth. Limnoria certainly swallows, and probably digests, the wood which it gnaws away'to form its burrow, but it is not known whether it has any other source of nourishment. The life-Iiistory is simple. As in most Crustacea, the sexes are

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separate and fertilisation is internal. The eggs are carried in a brood-pouch on the under side of the female until hatching takes place. The number in a single brood is generally from 8 to ] 2, but may be as many as 29. The young, on hatching, differ little, except in size, from the adults. Unlike the young of most marine animals, they seem to be of a less wandering disposition than their parents, for Hoek found that freshly attacked wood contained only full-grown individuals. The Gribble may occur near high-water mark, where it is only submerged for a .short period at each tide, but it is stated to be

Fig. 7 —Part of a Pide of Fir from Fig. 8.—Section of Wood Torquay Harbour, attacked by attacked by Limnoria. Teredo norvegica. The annual rings of the wood are cut The surface of the wood has been eaten away obliquely, and it can lie seen that the burrows of the Limnoria by Limnoria and Chelura, exposing the burrows penetrate more deeply into softer, of the Teredo, the shelly lining of which can he the light-coloured seen in many places. Much reduced. spring wood, while the harder, dark- coloured layers of autumn wood are not attacked till later.

most abundant between low water and half-tide mark. It has been found, along with Chelura, boring in the insulating covering of a submarine telegraph cable at a depth of 290 fathoms in the Mediterranean. It has been stated that it does not attack floating timber but there is some reason to believe that it may do so. The degree of salinity required by the Gribble is not exactly c 2 Original from and digitized by National University of Singapore Libraries 20 Marine Boring Animals.

known. Hoek found that, in Holland, an admixture of fresh water did not appear to disturb the animals unless the salinity fell below two per cent. They have been found alive a fortnight after the wood in which they were boring had been taken out of the water. Six species of the genus Limnoria have been described but some of them are not known to bore wood. The common L. lignorum is found on the coasts of Europe from the Lofoten Islands to the Black Sea and on both the Atlantic and the Pacific coasts of North America. In the Southern Hemisphere it has been recorded from the Falkland Islands, Port Elizabeth, Sydney, Wellington, and Auckland.

OTHER WOOD-BORING CRUSTACEA.

Another small wood-boring Crustacean is often found associated with Limnoria on the British Coasts and elsewhere. This is Ghelura terebrans (Fig. 9), which belongs to the Order Amphipoda although differing a good deal in appearance and structure from the Sand-hoppers which are the most familiar members of the Order. It is slightly larger than Limnoria and may be distinguished from it by the much larger and stronger antennae, by the pair of large tail-appendages (uropods) at the hinder end of the body, and by the sharp spine projecting from the middle of its back. The burrows made by the full-grown Ghelura are a little wider than those of Limnoria, reaching one-tenth of an inch in diameter. Owing to the fact that Ghelura is rarely FiG. 9. Ghelura if ever found apart from Limnoria (while terebrans, Female. £}ie latter is often found alone) it is probable The1 rma]eers' hi ti2at its importance as a destroyer of timber having much longer pag i,eeri underestimated. It is certain that tail -ap pen d ages uropods) and dorsal in many cases damage attributed' by engineers and others to the better-known Limnoria has been due to the two species working together (Fig. 10). Ghelura terebrans is found at many points on the coasts of Europe from Norway to the Black Sea, and also on the Atlantic coast of North America. It has recently been identified from Auckland, New Zealand, where it is associated with the European species of Limnoria. The only other species of the genus (Ghelura Original from and digitized by National University of Singapore Libraries Marine Boringo Animals.

Fig. 10.—Piece of Timber from Ryde Pier. Showing damage caused by Limnoria and Chelura. Much reduced.

insulae) was discovered by Dr. C. W. Andrews at Christmas Island, Indian Ocean, in company with another species of Limnoria. In various parts of the world, chiefly in the warmer seas, damage is done to structures of timber by another Isopod closely allied to Limnoria but of much larger size. This is a member of the genus Spliaeroma, the species of which are numerous and widely distributed. Only a few of them have the habit of boring in timber. In fact, although wood-boring species have been described from localities so widely separated as Florida, Brazil, the Cape, India and Ceylon, Australia, and New Zealand, it is considered by some authorities that all ;pIG ^ Spliaeroma these can be referred to a single species, terebrans. Sphaeroma terebrans, Bate (Fig. 11). It Enlarged.

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measures ^ths of an inch or more in length and its burrows are about 1th of an inch in diameter. It has, in a more marked degree than Limnoria, the habit of contracting its body into a ball, and preserved specimens are usually found in this attitude. Damage to timber has been mostly reported from localities where the water is probably brackish, or even, as in Florida (Fig. 12), quite fresh.

Pig. 12.—Piece of Pitch-pine Pile from Florida, bored by Sphaeroma terebrans.

GENEEAL REMARKS ON TIMBER BESTS.

It will be seen from what has been stated that the Shipworms and the boring Crustacea differ considerably in the way in which they attack submerged timber. The shipworm, making a minute opening in the surface of the wood, may penetrate far into the interior, and where the burrows are numerous they may seriously weaken a pile that shows but little external sign of damage. Since the animal never leaves its- burrow, the number of individuals that can penetrate from a small unprotected space (as, for instance, from a fault in the sheathing) is limited to the number of larvae

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that can find foothold in that space, but since the larvae are very minute, that number may be considerable. The length of the burrows may be very great, up to four or even six feet, and timber may he damaged up to that distance from the point of entrance. In contrast to this the damage caused by Crustacea is always superficial and is visible externally almost to its full extent; but as the washing away of the honeycombed surface exposes the deeper layers to attack, the damage is progressive until the wood is entirely destroyed (see Fig. 10). The hardness of the wood appears to be a matter of indifference both to the shipworms and to the Crustacea, oak and teak being attacked ai readily and destroyed nearly as quickly as the softer coniferous woods. The woods that are most resistant to attack probably owe their comparative immunity to the presence of essential oils (as in the Eucalypts) or alkaloids (as in Greenheart), but this resistance is only temporary, and every kind of wood that is commercially available has been found to be attacked sooner or later. Among those that resist best, the South American Green- heart (Nectandra Eoclioci), the Australian Jarrah (Eucalyptus marginata) and Turpentine (Syncarpia Iciurifolia) and the New Zealand Totara (Podocarpus Totara) may be,mentioned. The measures for the protection of timber from the attacks of marine boring animals fall into two classes : the first comprises those that aim at protecting the surface of the wood so as to prevent the entrance of the borers; the second includes methods' of impregnating the wood with substances that are poisonous or at least distasteful to the animals. Surface applications of pitch, tar, or paints or compositions of various kinds may be successful so long as the covering remains intact, but a small abrasion may lie enough to lead to serious damage. The process of " breaming " or charring the timbers of the hulls of wooden ships had as one of its objects the destruction and exclusion of shipworms, and a similar charring process has recently been recommended for the timber of harbour works. Sheathing with metal, as applied to ships, is of very ancient date. Greek and Koman galleys were sometimes sheathed with plates of lead* and a similar method was in use in the seventeenth century. Copper sheathing was intro¬ duced in the eighteenth century. In more recent years zinc, copper and Muntz metal have been used for sheathing piles, and casings of concrete or cement have also been used. All these

* Cecil Torr, " Ancient Ships," Cambridge, 1894, p. 37.

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methods are open to the objection that a very small unprotected space may admit enough shipworm larvae to destroy the interior of the timber. Against Crustacea they are more successful, as the damage caused is more localised. Another method adopted in piers and other harbour works consists in covering the surface of the wood with broad-headed iron nails (" scupper-nailing ")■• In this case the wood around each nail becomes impregnated with rust, which serves as a deterrent both to shipworms and Crustacea. Methods for impregnating the wood directly with metallic salts or other poisonous substances have been tried, but the only substance extensively used for this purpose is creosote. Even with this, lasting immunity is not attained, owing, probably, to the gradual washing out of the creosote from the wood. A heavy impregna¬ tion is essential to obtain good results and this is only possible with the softer kinds of wood.

ANIMALS BORING IN ROCK.

The marine animals that bore into rock are more nufiierous and diverse than those that bore into wood, but they are not often the cause of serious damage to engineering structures. Erom another point of view, however, they are of importance, since they aid in the disintegration of rocks on the coast and so hasten the encroachments of the sea on the land. Rock-boring species are known among Sponges, Echinoderms, Worms of various groups, Molluscs, and even Crustaceans; only a few of the more important can be referred to here.

ROCK-BORING MOLLUSCA.

The bivalved Mollusca (Lamellibranchiata or Pelecypoda) are characteristically a group of burrowers. The great majority burrow in gravel, sand, or mud, but a considerable number excavate sub¬ stances of greater solidity and attack even bard and compact rocks. The rock-boring habit is characteristic of certain families, such as the Pholadidae, but it has also been acquired by various species of unrelated families.

The species of Pholas (Eig. 13) and other genera of the family Pholadidae are among the best known. The Pholadidae are closely related to the Teredinidae, which they resemble in having no true

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hinge and no ligament uniting the valves, in having a blade-like process on the inside of each valve and in many other details of structure. They differ in the comparative shortness of the body, in having no pallets, no shelly lining to the burrow, and no knob on the ventral edge of the valves ; they have a varying number of additional plates between the margins of the valves. Pholas clactylus, the " Piddock," is the largest of the British species, its shell sometimes measuring as much as 5 or 6 inches in length, while its burrows may be a foot deep. There can be po doubt that the boring of Pholas is effected mainly, if not .exclusively, by the rasping action of the shell, which

Fig. 18.— Shell op Pholas clactylus. Fig. 14.—Valves oe Peiricolci pJio- Side-view on the left showing rows of sharp ladiformis (above) and Pholas teeth towards front edge above. Dorsal Candida (below). view on right showing additional plates between the valves. Reduced.

is provided with rows of spines or teeth towards the front edge. In specimens taken from soft substances like chalk or peat these teeth are slender and sharp ; in those from harder rocks they are blunt and rounded. The supposition that chemical means might be employed is excluded by the variety of substances in which species of Pholas have been found boring—limestone, sandstone, mica-schist, shale, peat, and even, occasionally, wood. In no case have they been found in very hard or compact rocks. The boring movements of the shell have been observed in the living animal. They consist chiefly in a twisting or rocking movement of the

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whole shell on the fulcrum formed by the sucker-like foot, the muscles from which are attached to the inner blades of the valves. There does not appear to be any rocking of the valves one upon the other as in Teredo. Some doubt as to whether this movement of the valves is the sole cause of the boring is, however, suggested by the fact that the outer part of the burrow, near the opening, which is in contact only with the fleshy siphons, greatly increases in size with the growth of the animal. A little shell which, from an examination of its outer surface alone, might easily pass for a species of Pholas, is now not un¬ common on the east and south-east coast of England. This is Pctricola pholadiformis (Fig: 14), a North-American species first noticed in British waters in 1890, having no doubt been imported along with living Oysters. It belongs to the Veneridae, a family widely distinct from the Pholadidae ; when the inside of the valves is examined they are seen to possess a hinge with interlocking teeth, a ligament and no inner blade. The resemblance which the shell bears to some species of Pholas, move especially to P. Candida (Fig. 14) which may sometimes be found burrowing in the same block of chalk with it, constitutes a remarkable example of convergence of characters associated with similarity of lg,abits. Very different in the form of its shell from the Pholadidae is the Mediterranean Date-shell, Lithophacja (or Lithodomus) lithopliaga. This is closely allied to the edible Mussel, belonging like it to the family Mytilidae. It has a thin and fragile shell, smooth and without teeth or spines, covered externally with a thick polished periostracum or cuticle. The facts that the shell is obviously unfitted for boring, and that the burrows are always in limestone or other calcareous rocks, suggest that excavation is effected by chemical means, and this has been confirmed by the discovery of a special gland situated in the mantle and producing a secretion that reddens litmus, this gland being absent in the related, non-boring forms. It is not unlikely that the thick periostracum may have the effect of protecting the shell itself from the solvent action of the secretion. Perhaps the commonest rock-boring mollusc on the British coasts is Saxicava rugosa (Fig. 15), belonging to the family Saxi- cavidae. This is usually found in calcareous rocks, often in lime¬ stone so hard and compact that it is impossible to suppose that the fragile shell can have excavated it by mechanical action. On the other hand it is stated that Saxicava is sometimes found in soft sand¬ stone, not calcareous, and not attacked by acids. If it be the case

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that the Saxicavci really excavates the cavities in which it is found in the sandstone it would show that the process of boring is not exclusively chemical ; that it is at least partly so may be taken as certain, although in this case no special gland has been found, and it has not been possible to demonstrate the emission of an acid secretion. The shell, which rarely exceeds an inch in length, possesses a rather thick periostracum, but this is usually much worn and would not protect the valves from an acid secretion if the latter were poured', out in any quantity. It is possible, however, that a solvent action may be exerted on the rock where it is immediately in contact with the secretory cells of the mantle, although tjie secretion is not in sufficient quantity to make its effect felt even a short distance away.

Pig. 15.— Saxicava rugosa Fig. 16. — Spliaeruma qzioycina, boring in Hard Lime¬ a Rock - boring Isopod stone. Crustacean.

One of,the valves is seen in side- Three specimens are seen above, two view above. Reduced. of them in the rolled-up attitude characteristic of the genus jSphcteroma. Below is a piece of sandstone showing the burrows. Reduced.

OTHER ROCK-BORING ANIMALS. Although certain Barnacles bore into limestone and coral, the only rock-boring Crustacean doing damage Of economic import¬ ance is an Isopod of the genus Sphacroma. This is Sphaeroma quoyana (Fig. 16), a species differing only in details from the wood- boring S. terebrans described above. It is reported from various localities on the coasts of Australia and New Zealand, where it burrows in soft sandstone or in claystone. Nothing is known as to

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the method of boring. It has been suggested that the Isopods were only found sheltering in cavities that had been bored by other animals, but according to Prof. Chilton (1919) there is no doubt that they themselves excavate the burrows in which they are found. The commonest of the rock-boring "worms" on the British coasts are Polychaeta. of the genus Polyclora (Fig. 17). The species are for the most part minute, but sometimes occur in vast numbers. The burrows are U-shaped and are commonly prolonged by tubular extensions of mud erected at each of the

Pig. 17.—Polydora ciliata, a Bock- Fig. 18.—Limestone Pebble bored boring polychaete worm. by Polljdora.

A. The worm extracted from its burrow. B. The mud tubes erected at the two open¬ ings of the burrow ; from one of them the two tentacles of the worm are extended. C. Diagrammatic section of the burrow with the worm in position. (A and B after M'Intosh. Much enlarged.)

openings. Polydora and its allies are usually found boring in shells, and in limestone (Fig. 18) and other calcareous rocks, but they are also found in shales and sandstone. Although there may be some abrasion of the rock by the horny bristles with which the feet of these worms are abundantly armed, it seems probable that this must be aided by chemical action before it could be effective in hard limestone.

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The boring sponges of the family Clionidae are very common in old Molluscan shells, but they also attack limestone rock. Oyster shells attacked by Cliona celata (Fig. 19) show numerous round holes about JTTth of an inch in diameter scattered over the surface and leading into branching passages in the thickness of the shell. When the shell has been all eaten away the sponge may grow into a massive form of considerable size. It has recently been shown

Fig. 19.—Oyster Shell attacked by the Boring Sponge, Cliona celata.

that the well-known Neptune's Cup sponge (Poterion patera), which reaches a height of several feet, is really the massive or full-grown form of a species of Cliona. When burrowing in limestone, Cliona does not, as a rule, penetrate far below the surface, but a specimen exhibited has been honeycombed to a depth of at least two inches. In organisms so inert as sponges boring by mechanical means would seem to be out of the question, but it has been seriously considered by some authorities who point out that the tissues of

Original from and digitized by National University of Singapore Libraries 3° Marine Boring Animals.

the Clionid® are more contractile than is usual in sponges and that the fine siliceous spicules (Fig. 20) of which their skeleton is composed would be capable of actingi on any but the hardest rocks. The fact that Clionidae only bore into shells or calcareous rocks strongly suggests, however, that they exercise a solvent action on the rock.

' Fig. 20.—Cliona celdta.

Above is a portion of the sponge obtained by dissolving away with acid the shell in whi it was burrowing. The turret-shaped projections filled the holes seen 011 the outside of the shell. The lower figure (after Topsent) represents a portion of one of these turrets more highly magnified showing the characteristic pin-sliaped siliceous spicules.

GENERAL BEMABKS ON ROCK-BOBING ANIMALS.

The destructive action of rock-boring animals is, as a rule, much slower than that of animals that bore in timber, and its effect on structures built of stone is probably, in most cases, negligible as compared with the damage due to waves and currents. Plymouth breakwater has been frequently referred to as an example of an engineering structure suffering damage from this cause. It appears

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that there is some difference of opinion among engineers as to the importance of tire damage, but there is no doubt that the limestone blocks of which the breakwater is built are extensively bored by many kinds of animals (Fig. 21). Dr. B. J. Allen stated some years ago in a report on the subject; "In a stone which has been injured through this cause, the outer surface, to the depth of about a quarter of an inch, is converted into a honeycombed friable mass through the ravages of the boring sponge Glionci cclata, whilst at

Fig. 21.—Section on Limestone from Plymouth Breakwater. The large cavities are the burrows of Saxicava. The honeycombed surface shows th action of the sponge Clionct, and here and'there fine tubes penetrating deeper into the stone have been produced by various Polycliaete worms.

frequent intervals larger holes, each of which may have a diameter of a quarter of an inch, and may pierce the stone to a depth of one inch, are formed by the boring mollusc Saxicava rugosa. To these two animals most of the damage is due, but in addition there are found a few holes bored by the mollusc Gastrochaena dubia, and many by the Polychaetes Dodecaceria concharum, Polydora ciliata, Polydora hoplura, and Potamilla rcniformis

.... Dodecaceria forms holes of oval or figure of eight section,

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which may penetrate for a depth of several inches into the heart of the stone; Polyclora ciliata forms small U-shaped burrows, open at each end, whilst P. hoplura makes similar burrows of larger size." It is somewhat surprising to find a Crustacean damaging the stonework of a harbour, but according to Chilton (1919) Sphaeroma quoyana does so at Wairoa, Hawke's Bay, New Zealand. In the harbour works at that place a kind of claystone, known as " papa rock," has been used to form walls constricting the river-mouth. This rock is burrowed by the Isopods "whose honeycombing operations have made the papa very light," with the result that the wall has, in places, practically disappeared. ^Blocks of concrete laid on the papa rock have sunk several feet owing to " the destruction of the underlying papa by the Sphaeroma." It has been stated that concrete is sometimes attacked by boring animals, and if this be the case it may become a matter of very grave concern for the engineer, in view of the increasing use of reinforced concrete for harbour works of all kinds. It has not been possible, hitherto, to obtain for the Museum any specimens of concrete so attacked. The selection of stone to be used in submarine constructions will usually be governed by other considerations than its liability to be attacked by boring animals, but it is clearly desirable to avoid, on the one hand, soft and friable stones that would give an opportunity to the mechanical borers like Pholas or Sphaeroma and, on the other hand, calcareous rock that might yield to 'the solvents probably employed by Saxicava, Gliona, and the like. Whether cement can be bored by animals or not it would be well to avoid using rubble of calcareous or friable rock for mixing in concrete.

LIST OF BOOKS AND PAPERS RELATING TO MARINE BORING ANIMALS.

Only a few of the more important works are quoted below. Most of them give references which will provide guidance for those who wish to pursue the subject further.

Allman, G. J., 1847.—" On Che.lv/ra terebrans, Pliilippi, an Amphipodous Crustacean destructive to submarine timber- works." Annals and Magazine of Natural History XIX., pp. 361-370, pis. xiii. and xiv.

Original from and digitized by National University of Singapore Libraries Marine Boring Animals. 33

Amsterdam Commission, 1860-1869.—"Verslag over den Paal- worm, uitgegeven door de Natuurkundige Afdeeling der Koninklijke Akademie van Wetensckappen." 158 pp., 4 pis., 4 tables. Amsterdam, 1860. The succeeding Beports were published in Mededeelingen der Koninklijke Akademie van Wetenschappen, XII (1861) p. 133: XIII (1862) p. 318: XV (1863) p. 293: XVII (1865) p. 74: (Beeks II) I (1866) p. 157 : III (1869) p. 207. Barrows, A. L., 1917.—■" An unusual extension of the distribution of the Shipworm.in San Francisco Bay, California." Univer¬ sity of California Publications, Zoology, XVIII, No. 2, pp. 27-43.'. Bate, C. Srence, and Westwood, J. 0., 1861-1868.—"A History of the British Sessile-eyed Crustacea." 2 vols. Baumhauer, B. II. von, 1866. " Sur le Taret et les moyens de preserver le bois de ses degats." Archives Neerlandaises des Sciences exactes et naturelles, I., pp. 1-45, pis. i.-iv. Baumhauer, E. H. von, 1869.—"Sur les moyens de preserver le bois des attaques du Taret." Op. cit. IV., pp. 160-166. Chilton, C., 1919.—" Destructive Boring Crustacea in New Zealand." New Zealand Journ. Sci. and Techn., II., pp. 3-15, 12 text figs. Coldstream, John, 1834.—" On the structure and habits of the Limnoria terebrans, a minute crustaceous' animal, destructive to marine wooden erections, as piers, etc." Edinburgh New Philosophical Journal, XVI., pp. 316-334, pi. vi. Forbes, E., and Hanley, S., 1853.—" A history of British Mollusca and their shells." Vol. 1.

Hatschek, B., 1880. " Ueber Entwicklungsgeschichte von Teredo." Arbeiten aus dem zoologischen Institut der Uni- versitat Wien, III., pp. 1-44, pis. i.-iii. Hedley, Charles, 1901.—" The Marine Wood-Borers of Australia and their Work." Report of Eighth Meeting, Australian Association for the Advancement of Science, Melbourne, pp. 237-255, pis. vii.-x. Hoek, P. P. C., 1893.—"Rapport der Comissie betreffende de levenswijze en de werking van Limnoria lignorum." Ver- handelingen der Koninklijke Akademie van Wetenschappen te Amsterdam (Tweede Sectie), Deel I., No. 6, pp. 103, xevi, 7 pis. Jeffreys, -J. Gwyn, 1865.—"British Conchology," Vol. III. d Original from and digitized by National University of Singapore Libraries 34 Marine Boring Animals.

M'Intosh, W. C., 1868.—" On the Boring of certain Annelids." Annals and Magazine of Natural History, ser. 4, II., pp. 276-295, pis. xviii.-xx. Qitatrefages, A. de, 1849.—" M6moire sur le genre Taret (Teredo, Lin.)." Annales des Sciences Naturelles. Zoologie, s6r. iii., XI., pp. 19-73, pis. i. and ii. " Memoire sur l'embryogenie des Tarets." T.c. pp. 202-228, pi. ix. Sellius, Godofredus, 1733.—" Historia naturalis Teredinis, seu

Xylophagi marini. . ." 4to. Trajecti ad Bhenum. Sigerfoos, Charles P., 1908.—" Natural History, Organisation, and late Development of the Teredinidse or Ship-worms." Bulletin of the Bureau, of Fisheries, Washington, XXVII., pp. 191-231, pis. vii.-xxi. Thompson, W., 1847,—"Note on the Teredo norvecjica (T. navalis, Turton, not Linn.), Xylophaga dorsalis, Limnoria terebrans and C'lielura terebrans, combined in destroying the submerged wood-work at the harbour of Ardrossan on the coast of Ayrshire." Annals and Magazine of Natural History, XX., pp. 157-164. Topsent, E., 1887'.—" Contribution il l'etude des Clionides." Archives de Zoologie experimentale et generale, 2e ser., V. bis, suppl., 4e mfemoire, 165 pp., 7 pis.

Original from and digitized by National University of Singapore Libraries INDEX.

Boring of Limnoria, 18; of Litho- Pboladidae in rock, 24; in timber, 17 ; phaga, 20; of Pholas, 25; of mode of boring, 25. Polydora, 28 ; of Saxicava, 20 ; of Pholas Candida, 26. ' Sponges, 29; of Teredo, 10. dactylus, 25. Burrows of Limnoria, 18 ; of Teredo, Piddock, 25. 11. Polycbaeta, rock-boring, 28. Polydora, mode of boring, 28. Calobate.s, 1G. ——- ciliata, 28, 31. Chelura in telegraph cables, 19. lioplura, 31. insulae, 20. Potamilla reniformis, 31. terebrans, 20. Poterion patera, 29. Cliona celata, 29, 31. Protective measures, 23. Cymothoa lignorum, 17. Rate of growth, Teredinidae, 14. Date-sliell, 20. Development of Limnoria, 19; of Saxicava, mode of boring, 20. Teredo, 13. rugosa, 26, 31. Lodecaceria concharum, 31. Sbipworms, 7. Sphaeroma guoyana, 27, 32. Pood of Limnoria, 18; of Teredo, 11. terebrans, 21. Sponges, mode of boring, 29. Gastrochaena dubia, 31. Gribble, 17. Telegraph cables attacked by Chelura, 19; by TAmnoria, 19; by Xylophaga, Limnoria, burrows, 18; development, 14, 17. 19 ; food, 18 ; in telegraph cables, Teredinidae, 7 ; burrows, 11; develop¬ 19; mode of boring, 18; structure, ment, 13; food, 11; mode of 18. boring, 10; pallets, 8; rate of lignorum, 17. growth, 14 ; shell, 9 ; structure, 8.

■—— terebrans, 17. Teredo diegensis, 15. Lithodo?nus, 2G. dilatata, 14. Lithopliaga, mode of boring, 26. megotara, 15, 10. lithopliaga, 26. • navalis, 8, 14, 15, 10. norvegica, 9, 15, 1G. Martesia striata, 17. Xylophaga in telegraph cables, 14,17 Nausitora, 16. dorsalis, 17. Xylotrya, pallets, 8; rate of growth, Pallets of Teredinidae, 8. 14. Petricola pholadiformis, 26. ■ gouldii, 14.

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Economic Pamphlets. No. 1.—The House-Fly as a Danger to Health. Its Life- history, and how to deal with it. By Ernest E. Austen. Second Edition. Pp. 12: 2 plates (containing 4 figures), and 3 figures in text. 1913, 8vo. Id. (postage Id.). No. 2.—The Louse and its Relation to Disease. Its Life- history and Habits, and how to deal with it. By Bruce E. Cummings. Pp. 16: 1 plate (containing 2 figures), and 2 figures in text. 1915, 8vo. Id. (postage Id.). No. 3.—Fleas as a Menace to Man and Domestic Animals. Their Life-history, Habits, and Control. By James Water- ston, J3.D., B.Sc. Pp. 21: 1 plate and 6 text-figures. 1916, 8vo. Id. {postage Id.). No. 4.—Mosquitoes and their Relation to Disease. Their Life-history, Habits, and Control. By E. W. Edwards, B.A. Pp. 20 : 6 text-figures. 1916, 8vo. Id. {postage Id.). No. 5.—The Bed-Bug. Its Habits and Life-history, and how to deal with it. By Bruce E. Cummings. Second Edition. 1918. Pp.20: 7 text-figures. 8vo. 2d. {postage Id.). No. 6.—Species of Arachnida and Myriopoda (Scorpions, Spiders, Mites, Ticks, and Centipedes) injurious to Man. By S. Hirst. Pp. 60: 26 text-figures and 3 plates. ' 1917, 8vo. 6d. {postage 2d.). No. 7.—The Biology of Waterworks. Second Edition. By R. Kirkpatrick. Pp. 58 : 18 text-figures. 1917, 8vo. Is. (postage 2d.). •No. 8.—Rats and Mice as Enemies of Mankind. By M. A. C. Hinton. Pp. 63: 6 text-figures and 2 plates. 1918, 8vo. Is. {postage 2d.). No. 9.—Birds Beneficial to Agriculture. By E. W. Erohawk. Pp. 54 : 22 plates. 1919, 8vo. 2s. (postage 2|d.). No. 10.—Marine Boring Animals Injurious to Submerged Structures. By W. T. Caiman, D.Sc. Pp. 35 : 21 text- figures. 1919, 8vo. Is. (postage 2d.). A pamphlet on "The Furniture Beetle " is in preparation. Economic Leaflets. No. 1.—The Danger of Disease from Flies and Lice. Second Edition. Pp. 4. 1918, 8vo. Price : Id. for- 3 copies {postage Id.), 2s. 6d. for 100 {postage 5|d.). A leaflet on "The Danger of Disease from Fleas and Bugs " is in preparation.

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January from 2 to 4

February 1 to 14 .. A J J 4.30

„ 15 to end „ 2 5 5 5 *>./ March 5.30 M „ 2 J)

...... • „ 2 it 6

May to August (inclusive) „ 2.30 5 5 7

September „ 2 J> 5.30 October „ 2 5J 5 November and December ,, 2 J) 4

The Museum is closed on Good Friday and Christmas Day.

By Order of the Trustees,

S. F. HAEMER, Director.

LONDON' PRINTED BY WILLIAM OLOWES AND SONS, LTD., DUKB STREET, STAMFORD STREET, Original from and digitized by National University of Singapore Libraries