Embryology of Echinoderms

Home , Melonites (Echinoid)

EM B R Y O L O G Y O F ECH I N O D ER M S .

B Y A L EX A ND ER A GA S S Z . ‘ I

M HE M I ICA A DEMY V L. IX . FRO T ME O RS OF THE A MER N A C , O

n 2d 1 864 . Comm u icated February ,

P ub lishe d Alarch , 1 864 .

M EM O I R S

O F TH E

A M ER I C A N A C A D EM Y .

On th e Embryology of Ech inoderms .

B Y A L EXA N D ER A GA SSIZ .

Co mm un icated Fe b u a 2d 1 8 64. r ry ,

THE following account of the embryology of a few of our Echinoderms , though by

s o f no means complete , will ﬁll everal the gaps hitherto existing in the knowledge of

" th e development o f Echinoderms ; and in the h Ope that something may be added to

o u r s n o f o f o f under tandi g the general plan development Echinoderms , it is here given

n o s h o w is i its present c ndition , in order to how far the plan of development identical ’ f I s l ih . O h i the di ferent orders of Echinoderms ha l take up in turn the Echinoids , p

s ff a uran , and Holothurians , and then compare these di erent larv e with what we know

o f o u r s se e h o w f already of the development common Starﬁ h , to close the agreement o

o f o f n is s s the mode formation the you g Echinoderm in these four orders , and to ati fy

s o n s " ourselves how true are the uggestions made at that time , a very uperﬁcial ac

o f A ste racan th io n quaintance with any other Echinoderm larva except that , concerning f f the function of many o the organs o these wonderful larvae .

E E B TOX OPN UST S D RO A CHIEN SIS A G .

T h e larvae o f our common Echinus resemble most clo sely,in some of their earlier

tes livi us A . o n To m neus . VII . stages , those of p d g , ﬁgured by Muller Plates VI and of

* M lle r w w his fourth Memoir . The ﬁgures which ii gives correspond ith hat I have

‘ i n ic E h in U E J . b e r Larv e i u d d s de r c o dcrm n . h Uc c A b amll n . M LL R , die Metamorpho e Vierte u g Be r

1 85 2 . lin ,

VOL. IX . 2 ON TH E m rs ar o no o r o r E CH IN O D ER M S .

observed in larva obtained by artiﬁcial fecundation . He succeeded in tracing them

is as as . for about three weeks , which not quite long I have kept them alive Muller

h as n o t o f s s unfortunately given us any ﬁgures the very ﬁrst stages of thi specie , nor h as he found the adult larva swimming about immediately before the ab sorption o f the

s u s Pluteus . The series of ﬁgure found in this paper will give a more complete idea

o f f s o f o f s s the di ferent pha es growth one specie of Echinu , than can be gathered from a

s comparison even of the different species which Miille r h a investigated . It will enable

u s o f s s s to trace the order appearance of the arms of the Pluteu , and the la t change

which the larva undergoes immediately before the young Sea- urchin has resorbed the

whole framework o f the Pluteus .

The - process o f segmentation o f the yolk is entirely similar to what we observe in the Starﬁ sh ; the main differences in the eggs are simply o f proportion between the

- s relative size of the yolk m ass and the outer envelope . My ob ervations agree with

E ’ " o f the account of the segmentation given by D e rb é s. The formation the Rich tun g s

- Blasch en is very easily followed in the Sea urchin .

s s The yolk contract omewhat immediately after the fecundation takes place , and we

o f might repeat here , word for word , the description the changes which the yolk und

Starﬁsh e s s o f s goes in the , and have the hi tory the change during the segmentation o f

o f the yolk o f an Echinus . Fo r an account this I would refer the reader to the ﬁfth

o f N U volume the Contributions to the atural History of the nited States , by Professor

ss . o n s s Aga iz The embryo , e caping from the egg , resemble a Starﬁsh embryo , and it

o n e f would greatly puzzle any to perceive any di ference between them . The forma

o f o f a so h a us - s tion the stomach , the p g , the intestine , and the water tubes take place

s f in exactly the same manner as in the Starﬁsh , the time only at which the e di ferent

s ff s organ are di erentiated not being the same. We have thu very early in the history o f these two orders differences which to a practised eye tell at once to which o f them f i the young larva belongs. What is a particularly important di ference s the forma tion in Ophiurans and in Echinoids o f calcareous rods at an early period o f the larval

condition .

Th e em r o a ter i ts esca e om th e e b y f p fr gg . In the spherical embryo soon after its escape from the egg we perceive a thicken

o f o f s is ing the walls at one the poles ; a depres ion then formed at this extremity ,

s an d which become more and more marked ; T the wall then turns in , a small cavity

° E . . . i . . . . D ER B n 3 III. 8 0 1 47 . S Ann (1 Sc e . Nat Ser V p 8

‘ ﬁ s. 4 5 1 m A ste racan th io n . . . . VI . 1 4 1 8 63 See g and of y paper on in Proc Am Acad , Vol , April , , which

s s repre ent the corre ponding stages of the embryo of the Sta rﬁsh . ON THE EM B R YO LOGY OF E CH I N O D ER M S . 3

n s d is formed , which goes on i crea ing in length until we have a hollow cylinder ( )

f 1 2 s . o . 6 extending half the length the larva , as in ﬁgs and , which corre pond to ﬁg

. 1 of my paper referred to above . In the proﬁle , ﬁg , we notice the same tendency

v in the digestive ca ity (d) to incline towards the lower side , after the dorsal portion l i vm b e re le d . has increased more rapidly, g g the anal part of the larva a appearance

s . 3 In a omewhat older stage , ﬁg , the digestive cavity is still longer , and almost touches

f s - the lower side . We notice a di ference between the Starﬁ h and the Sea urchin in

o f t s o s . the time formation of the alimen ary canal , the tom ach , and the e ophagus In the Starﬁsh the mouth is formed before the differentiation o f these organs takes place ;

while in the Sea- urchin the m outh is not formed until the alimentary canal and the

- a so h a u s as s . . p g , as well the water tubes , are quite di tinctly deﬁned (See ﬁg What is also peculiar to Echini is the pre sence of large masses of yolk- cells along the sides o f o f the digestive cavity , indicative the great changes which take place at the points

- s where these masses of yolk cells are most numerous . We have ob erved that the yolk cells are always present wherever any new organ is developed ; in these larva the

appearance of the water- tubes is preceded by an accumulation of yolk- masses at the f o f s . o . extremity the dige tive cavity (see ﬁg and the place the limestone rods , ﬁg

’ 4 r s s o f - in , , is ﬁrst seen ﬁlled by clu ter these yolk masses , the midst of which the rods

s a f are depo sited . Rod extending into the rms are characteristic o Echinoids and

ra o f o r Ophiu ns ; we ﬁnd nothing the kind in Starﬁsh Holothurian larva .

. 4 d In the next stage , ﬁg , the original cylindrical digestive cavity has already a e

f d o f 0 cided tendency to di ferentiation , the walls of the stomach ( ) and the oesophagus ( )

o f f o being very di ferent thickness from , the pouches which are to become the water

' w w o f tubes ( ) project far beyond the outline the digestive cavity . The limestone ’ ’ rods (7 r ) can faintly be distinguished from the mass o f yolk - cells which surround

them . The calcareous cells which take such a great prominence in older larva (see

1 o f . 3 ﬁg . 9) make their appearance as early as the stage ﬁg ; they are quite large in

4 . s the condition represented in ﬁg . The strong contra t which already exists between the different parts o f the digestive cavity is still more apparent in a stage but slightly

. 5 . s more advanced , ﬁg The dor al portion of the larva has up to this time been grow

o f ing most rapidly, changing the outline the larva , particularly when seen in proﬁle ;

e in the subsequent ﬁgures , the outline , when se n from above , is also undergoing great

. 6 changes . The larva assumes a more rectangular shape (ﬁg ) when seen either from

o r w - above from belo . The water tubes are almost separated from the digestive cavity,

0 0 which has been divided into three very distinct regions ( , d , , ﬁg . the limestone

- ff T . 5 o rods , simply shaped before , ﬁg , are sending small processes , and the chords B OL G CH IN D R S 4 ON THE EM R Y O Y OF E O E M .

v . of vibratile cilia ( , which were a simple button ﬁg are quite stout , project

. is n 6 v . ing beyond the ge eral outline when seen from above or below (ﬁg , ) It at this a so h a u s advanced condition only that the p g touches the lower surface , previous to

o f the formation the mouth , which takes place only when the larva has reached the

A . 6 . 7 s h o w o f . 9 . condition fig view of fig seen from the anal extremity , fig , hows

- . 8 its . far it has lost cylindrical shape and become wedge shaped In ﬁg , which is the

s o f same larva seen in proﬁle , the indentation which indicates the po ition the mouth (m ) h as changed somewhat the even outline o f the lower surface ; there is a marked

n a bendi g of the alimentary canal , bringing the anal opening ( ) still nearer the lower

o f s . 1 a m surface . In fact , ince the ﬁrst formation an opening in ﬁg ( ), which is at once strictly mouth and anus , there is a continued tendency to bend the anal part o f

s the dige tive cavity towards the oral surface , even while this single Opening perform s

o f the functions mouth and anus , during the period which precedes the formation o f

a SO h a u s the mouth , after the alimentary canal , the true stomach , and the p g have ff been differentiated . This is somewhat di erent from what we notice in the Starﬁ sh embryo , where the mouth is formed before the anus has been much bent from its

"6 original po sition .

’ ’ The large accumulations o f yolk- masses round the rods r r cannot fail to be noticed

s s . 6 7 8 . n in the stages ju t de cribed , ﬁgs , , This contrasts striki gly with the Starﬁsh

rv a o f o f is la , in which we ﬁnd nothing the kind ; the body the young embryo quite

its s remarkable for great tran parency , which only increases with age , while in the

Echinus larva the great accumulations o f yolk- mas ses renders them somewhat opaque

s o f ad even in their early stages , and the increa e calcareous cells in somewhat more

v an ce d fi s. 1 7 1 9 f forms , as g , , makes it more di ficult than in the Starfish to trace

- accurately the minute changes which the rods and water tubes undergo . We now 1 f s ﬁ s . 9 0 u s come to condition , g and , which are su ﬁciently advanced to enable by

as ﬁ s 1 6 1 7 1 9 e comparing them with still older forms , such g . , , , to form a corr ct idea

o f s s ﬁ s. 9 1 0 to the mode of tran formation from the hape of g , , the complicated larva

20 . as s . repre ented in ﬁg I merely refer to this comparison in a general way, in the

o f ff explanation the di erent stages it will be carried out more fully , to call attention to

u s f the periods which ﬁrst give a clew to the development of the di ferent parts , by

u s s showing plainly which portions of the embryo mu t assume a great prominence ,

s u and obtain a more rapid development than other , to pass gradually thro gh the stages ff . 9 which are hereafter ﬁgured . In ﬁg the di erence in the rapidity of the development

. 8 . . . . VI . . See ﬁg , Proc Am Acad , Vol , q uoted above B L OF CH N D R S ON THE EM R YO OGY E I O E M . 5

’ ’ — - - o f w w . w the two water tubes , , is quite striking The left water tube ( ) left when

as s seen from the aboral side , the anal extremity being turned down in the e ﬁgures

is s s its fa t pu hing through the mass of the larva , and ﬁnds way to the surface at about

1 5 - the condition represented in ﬁg . , where the water pore, the madreporic body , allows

- e the water to enter freely into this water tube . In a somewhat mor advanced larva ,

. 1 0 seen obliquely from the oral side , ﬁg , we can trace the mode of development of the

o f h chord of vibratile cilia ; it is formed a single continuous line , extending round t e

o t s mouth ; it forms but a single shield , and n two as in the Starﬁsh , where the ﬁr t trace o f this chord is the appearance of two separate arcs formin g eventually two dis

n tinct plastrons . The little larva looks in this condition like a quadra gular pyramid

’ ’”

s . e e with a rounded apex and rounded angles at the ba e The corners of the base ,

o f o f a . 9 to are the origin the ﬁrst arms the larv (ﬁgs , Owing the great increase

o f o f a n the dorsal and oral parts the larv , they cha ge their general appearance very

ﬁ s 1 1 rapidly . (See g . , As the intestine becomes more distinct from the stomach ,

1 1 c d m . m the angle which their axes make grows ore acute (ﬁg , ) ; the mouth ( ) is s a so h a u s 0 removed further from the anus . The wall of the p g ( ) are now capable of considerable expan sion and contraction ; they are much thinner than those o f the

s o r . 1 2 . 1 1 s inte tine stomach . Fig , which is ﬁg seen from the oral side , show the

’ o f i o f e o f course the vibrat le chord , the position the arm s , the great size the rods

f o f with their branches , and the di ference level between the Opening of the mouth

1 1 s o f and anus . From an examination of ﬁgs . 1 and 2 the po ition the rods can be

’ o n e e determined , main part extending from the anal extremity to the arms , another

' 1 1 e o ff h extending in a curved line (fig . ) from to and sending a small branc which h t e s s . runs between anu and the dige tive cavity (fig This will , perhaps , be more clear on examining the larva in such a way (fig . 1 3) as to bring the vibratile chord into 1 n o t f s . 0 the field ; this stage does di fer materially from that repre ented in fig , the chan ges which have taken place defining the arms more sharply by the indentation s o f

(e s the vibratile chord . The intestine , the stomach , and the ophagus are clearly dis

i is - t n u h e d f o f . n o t g by the di ferent character their walls The water tubes are united ,

s s ff th e and have not increa ed in size . This condition present a material di erence in

degree o f development when compared with the corre sponding stage o f a Starﬁsh (ﬁg .

1 1 - o f , Proc . Am . Here the water tubes occupy the most important portion

- h th e s the larva , while in the Sea urc in larva most triking characteristic is the amount o f room taken up by the stomach and (e sophagus compared with that occupied by th e - water tubes .

1 4 l a In the subsequent stages (ﬁgs . and the Echinus arv have reached forms 6 ON TH E EM BR YOLO GY OF ECHINODERMS . which are already more familiar to u s from the drawings o f Muller ; they resemble closely some of the ﬁgures given by him Of Toxop n eustes lividus in his fourth Memoir . A good deal o f allowance must be made for the differences Of outline between the

ﬁgures given here and the drawings o f Muller . From the evidence Of the drawings

h im s . themselves , it is plain that nearly all the specimens drawn by are compres ed I have endeavored to represent these larva as they appear swimming about ; it is by no means an easy task to follow them in their almost unceasing movements with the

n to s magnifyi g power required introduce the nece sary details , but I trust I have suc cee de d in giving a tolerably accurate idea o f their appearance in these outline draw ings. In a larva during the tenth day after fecundation (ﬁg . the most important ’ o f e changes are the increase the arms , and the formation of rudiments Of another ” o f s e v Millle r h as accu m u pair arm , ; the vibratile epaulettes , as called the peculiar

’ o f e lation vibratile cilia situated between the base of the adjoining arms , make

s s . their appearance at thi tage It is easy to follow them from their origin , when they 1 4 1 ﬁ s. 5 are simply a thickening of the vibratile chord g , , until they have passed 1 6 1 1 s s . 7 9 through the succes ive stages repre ented in ﬁgs , , , to attain the great size

s . 20 n ob erved in ﬁg , when they appear in certain positions as having no connectio

o f whatever with the vibratile chord , and to have originated independently the main

M lle r n o t o n . ii chord had traced their development , and laid great stress their pres

ff - ence in distinguishing the di erent species o f Sea urchin larva .

o f s n o w With the development the arms , the inte tine loses its former shape ; it has

o f s assumed the appearance a large elliptical receiver with thin walls . The tomach is

- - - somewhat dumb bell shaped , and the left water tube connects with the surrounding

- i b ts . water, through the water pore , having pushed way to the surface The rods keep

1 5 - pace with the growth of the arms , ﬁg. the water tubes have not increased in size ;

th e they are still two distinct bodies . The anal part of the outline of larva is quite

is pointed ; the aboral side regularly arched , with a slight depression at the point

- b 4 1 . o f . s where the water pore Opens , , ﬁg The Opacity the larva has increa ed to such an extent that it becomes impossible to deﬁne clearly the outline o f the water- tubes

s ﬁ s 1 4 1 6 in the stage which come between g . and . I am unable to state po sitively

- whether the two water tubes are united in this and Older larva . All I could distinctly see was the great increase in size Of the water- tubes but at the same time it becomes

to s o f a puzzling matter trace the limit these tubes , owing to the delicate walls which

fin e bound them . Their presence can only be traced by the line which runs across the o s - b e ophagus from each side , and by the water pore and the tube leading to it ; , fig . 1 6 . o f 1 In a profile view a larva considerably Older than that represented in fig . 5 , the ON THE EMBRYOLOGY OF ECH INODERMS . 7

1 6 s . epaulette , ﬁg , have assumed a more independent position , forming a curve somewhat similar to the are from which the median anal arms o f the Brachiolaria

" th e o u t e are developed third pair of arms bulges quite prominently , , when seen in

" o f e proﬁle the fourth pair arms is visible , the rod which eventually extends in the ” o f is r i a interior it a straight rod ( ) w th a slight point in the middle , t present discon

o f n e cte d from the remaining part of the calcareous framework . This set rods and the

" e n fork which extends into the arms , take their origin independently from the mai rod , extending from the anal part round by the mouth , from which branches are sent

’ ” e r into the arms and The rod ultimately combines with the main system , but

’” r s s s o f the rod always remain separate from the other . The po ition these rods is

1 s better understood from ﬁg . 7 when een from the aboral side .

1 is . 7 is The stage represented in ﬁg particularly important , as it at this time that we notice the ﬁrst trace o f what I suppo se becomes the tentacular pentagon o f the

- th e - t young Sea urchin . On left water tube we notice a very prominent loop , , which , from its resemblance to the tentacular loops of Brachiolaria and from its position on

- n - the water tube connecti g with the water pore , I have no hesitation in considering to be

’ 1 2 o f II f lle r s . . V . o Mii the first tentacular loop formed Compare figs , , Plate seventh m * f Me oir, where he figures a similar tentacular loop in two di ferent stages of develop

n Miille r s ment ; unfortunately , there is nothi g in the text to explain what con idered

f i a it to be . The relation o this loop to the madreporic body s perfectly pl in in this 1 . 8 same larva seen from above as it is ﬂoating in the water , ﬁg , the epaulettes

’ ” th e s o f e e appearing like great ﬂaps extending between ba e the arms and , in con tin u atio n Of the chord o f cilia extending along these arms .

1 - l Figs . 1 7 and 8 are larva twenty three days O d during the next four days no

o f change any importance could be perceived the tentacular Ioop remained the same ,

s the arm alone increasing in size , and a few dark pigment spots appeared in the arms .

- U s . nfortunately, at the end of the e four weeks the young Sea urchins all died I have

s only once ucceeded in keeping them such a long time , and that was during the coldest i . n winter weather In the attempts made the spring , whenever a warm day came , it was n l sure to kill everythi g ; while in the summer , though the faci ities I had were

a o r inﬁnitely greater , I never could keep these larv alive more than three four days .

- The Sea urchins spawn during the whole year . Successful artiﬁcial fecundations have D been made in ecember , January, and during every month from that time till the middle of October .

M L E U L R J . G Se e i e llarv e n . i 1 855 . , Ueber die attungen der g Berl n , ON 8 THE EMBRYOLOGY OF ECHINODERMS .

The remaining Ob servations of this paper were all made from specimen s caught swimming o n the surface o f the water ; this applies to the fully- formed Sea- urchins

as as a s . 28 well the larv , only the most advanced pecimens (ﬁg ) were found thrown up o n the beach after a storm , attached to Laminaria . The specimens Obtained in

o f this way , the various stages which were traced until there could be no doubt to what species they belong , connect so nearly with specimens obtained from artiﬁcial

to ﬁll u s fecundation as .to leave but few gaps , in the larval condition , to give all

- s a their transformations . The Sea urchins rai ed from larv caught swimming freely about were kept in conﬁnemen t until they had attained the size o f some Of the more

- 26 2 . . 7 o u r advanced nomadic Sea urchins, ﬁgs , This can leave no doubt to which of two species Of Echinoids these larva should be referred .

1 s . 9 The next oldest larva , which is ﬁg , hows that since the last stage represented

o f 1 9 the principal changes have taken place in the oral part the larva , ﬁg . ; the arms

” " e e s s , e pecially have increa ed greatly in length , the outline Of the anal extremity is

o f somewhat rounded , the rod which runs along its edges is made up short, stout pieces

o f o f s with strong pointed projections , and the rods the arms are composed three rod connected together by transverse spokes ; it requires clo se examination to distinguish this . On the aboral side two very prominent spurs project over the stomach , somewhat

’ ” w o f o f e e belo the point of junction the rods the arms , , Additional tentacular loops have been formed ; we can distinctly trace three o n the surface of the left water

’ tube w ; the outline of a part o f the right water- tube (to) shows great increase in the

- - o f . . 20 volume the tube In an adult Sea urchin Pluteus , ﬁg , the Sea urchin has encroached so much o n the anal extremity as to conceal the shape o f the digestive

h e o f . t n cavity The spines are so large, that we are unable to trace position the te tac ”

. v ular system ; the anal Opening is very conspicuous The vibratile epaulettes , , are remarkably powerful . The arms have attained nearly the same length . The vibratile chord has been twisted in such a manner as to assume the appearance o f binding an ’ ” ” e e e s anal and an oral plastron , of which , , and are respectively the arm ; the mode Of formation of the chord and Of the arms shows that all these arms in reality

s 1 2 o n e e e . belong to plastron ( ﬁgs , notwithstanding the great resemblance to the

s s o f two di tinct plastron a Brachiolaria . Two very prominent black spots are seen in

’ ” s e e s Miille r h is P luteus uadrim the arm , , similar to tho e observed by in q acula tus a few small spots are scattered over the other arms . The Pluteus ﬁgured here in its natural attitude does not undergo any further changes of form it n o w enters a stage when the Sea- urchin goes through its greatest transformations ; these unfortunately

o f cannot be followed , owing to the Opacity the larva . TH E O O O N EMBRY L GY o r ECHIN O DERMS . 9

The presence of rod s in the plutean forms Of Ophiurans and Echinoids of course restricts con siderably the play of the arms in assisting the motion o f the larva . The

s arm cannot be bent and twisted in the graceful manner so peculiar to Brachiolaria .

o f s s o f . They are only capable opening and hutting like the rod an umbrella . Fig

s 2 1 . 20 s , which is ﬁg een from above , when left in its natural attitude , hows the extent

s to which the arms can be pread . This does not prevent the larva from moving quite

o f s m rapidly by means of a kind gliding motion , in which the vibratile epaulette perfor

s. t an important part in propelling the Pluteu While moving , the anal extremi y is

s usually kept below , as in the po ition which has been given to all the ﬁgures in this

is n atural os ition . Memoir, which their p Previous to the time when the anal extremity

- ﬁ 1 is loaded down by the presence of the Sea urchin ( gs . it is quite common to

ss d re ctio n f see them moving in every po ible j , so that it would be di ﬁcult, from a knowl o f s a to s edge the earlier t ges alone , ascertain with preci ion what the natural attitude is although we notice even in the early periods a very strong tendency to assume the

a s ss natural po sition o f the adult larva . The larv al o a ume during their movements the oblique position described in Brachiolaria ; this seems characteristic o f all the

a h Echinoderm larv I ave had occasion to examine , whether Ophiuran , Holothurian ,

o r A ste rian . A o f . 2 2 Echinoid , natural proﬁle view an adult larva (ﬁg ) cannot be s made with great accuracy , and the outline here given is added imply to show the

s s o n s position of the arm ; rotating as they do almo t continually their vertical axi , we

l s catch on y pas ing glimpses of the exact proﬁle outline . The only adult larva ﬁgured

iil Of h is s in proﬁle by M le r is on Plate V . eventh Memoir .

. 20 fo r An adult Pluteus , in the condition of ﬁg , requires several weeks the co m

i n o f o f ple t o the Echinus and the absorption the plutean framework . The Echinus

’ s o n o f e e encroache gradually the anal extremity ; the base the arms , and is soon lost

o f o f - in the midst the spines the young Sea urchin , which are arranged in a conical 2 s s . 3 . open piral wreath urrounding the mouth , ﬁg While this encroachment o f the

is o n o s s anal extremity going , the e ophagus has contracted to uch an extent that the ” s rm s e ba e of the oral a , , is brought directly in contact with the anal vibratile chord . D uring the process of resorption the arms have lo st their mobility ; they appear like

s helples rods , stretching at every conceivable angle from the Pluteus , which has lost

its . 23 . entirely former symmetrical appearance , ﬁg

h u e Th e young Ech inus af ter th e R eso rp tion of t e P l t us.

o f * The ﬁgures given by Miille r on Plate III . his ﬁrst Memoir represent several

M uL L ER J . L s O h iure n . 1 8 4 a Ueber die arven und die Metamorpho e der p und Seeigel Berlin, 8 . 2 VOL . xx . 1 0 ON TH E EMBRYOLOGY o r Ecm uo nnnms.

Echinoid l arva in which the young Echinus h as ab sorbed more o r less o f the plute an

o n s Of a is frame . From what I have observed everal these larv , the Pluteus as com

N o t s ple te ly resorbed as is the case in the Brachiolaria observed by me . a ingle part o f the framework is thrown o ff ; this process o f resorption begins at the base o f the arms ; they are thus gradually shortened , the rods apparently melt away before our

s o f s eye , the extremity the arms is the la t to disappear , and immediately before the

s is s s o f time when the young Echinu freed from the plutean appendage , the extremitie

s as all the arms are till there , as perfect when these appendages stretched symmetrically

o f s o f Miille r s o n both sides of the longitudinal axis . From many the ﬁgure him elf it is a h as s s s o f evident that , in the larv he ob erved , the young Echinu re orbs the whole

s h as . the framework , and does not separate from it by losing the arm , as he stated

h i s f . s . . V s . . V . o See Plate III , IV , , VI the ﬁrst , and Plate III of eventh Memoir The

o f w as lst o f larva represented in ﬁg . 20 this paper kept in conﬁnement from the

20 th o f N th e October to the ovember before every trace of arms had disappeared , and

- f . 4 the young Sea urchin had assumed the appearance o ﬁg 2 4. Fig . 2 was drawn from

o f s a a specimen found ﬂoating o n the surface in the middle June . Thi young Se urchin bears a striking resemblance to a youn g Ech in o cidaris ﬁgured by Muller o n i o f h s . Plate IV . seventh Memoir The development of the separate parts is very dif

f in To xo n ste s fe ren t two . o e u in the The number spines is much greater our p , and

s n they are o f an entirely different shape . Pedicellaria are likewi e present i Echino * cidaris ; these do not make their appearance till a much later period in o ur young

- is O . 28 . f Sea urchins . (See ﬁg , p ) What particularly characteristic these earlier stages o f - is s o f the young Sea urchins the great ize and small number the spines. Their

is s o n is position al o peculiar ; they are all placed the edge Of the test , which exceed

l do h o r f i n Po a. o g y ﬂat. (Compare this with p ) Five the tentacles are strikingly

o f prominent , equalling in length the diameter the shell ; they are also remarkable fo r is their great thickness , and the presence of a calcareous ring in the sucker, which

a ﬁ h e s St r s . entirely wanting in young A similar calcareous ring is ﬁgured by Muller,

h W - The function of pedicellaria as long been a puzzle to naturalists. hile watching a Sea urchin which was s its x s I s s s in te ram b u di charging e crement , noticed that the pellet alway moved in deﬁnite path , down the

- lacral s s s Off s . O x s m ss I pace , till they were pu hed from the te t n e amining thi with a agnifying gla , could dis tinctly se e the innumerable pedicellaria hard at work s eizing in their tiny prongs the pellets which they

n it pu shed down the interambulacral areas. If by cha ce a pellet found s way into the ambulacral zone and

s s w as s came in contact with the ucker , it immediately eized by the ambulacral pedicellaria and thrown back

t s into the interambulacral zone to move on in i s accu stomed path . The pedicellaria are more numerou in the

. s x u s d s interambulacral zone than in the ambulacral Thi will e plain the f nction of the e pe icellaria, at lea t for

- Se a s as s s. urchin , that of cavenger o ON THE EMBRYOLOGY OF ECHINODERMS .

. . 1 3 2 s Plate IV fig , seventh Memoir, and Plate VII . fig . , fir t Memoir . The whole

is - n abactinal surface thickly covered with dark crimson pigment cell s. The you ger

s s s o f se 1 6 e . A o . 1 w spine re emble tho e the young Starﬁsh ( ﬁg , Proc . Am . , . hile

s - s s n the more advanced spine are not fan haped , but lightly pointed , remindi g us o f

f - o . i o n as . 26 spines Cidaris On turning this Sea urch n its actinal side , in ﬁg , we

o f o f s as ﬁnd near the base each the ﬁve large tentacle four others , which are not

o f s advanced , and are incapable expanding beyond the edge Of the te t .

s are o f Additional pines formed on the abactinal side of the test older specimens (ﬁg . so s o t its that they cover the whole of that urface , and are no l nger limi ed to edge ,

. 24 s as in ﬁg ; the large spines become more pointed , the tentacle grow slender , and

d o f o dd they can all expand beyond the e ge the test . The tentacle expands and con

s s as s tracts to a remarkable extent , ometime much as three time the radiu s . The four

o f s other tentacles are somewhat more stout , and not capable such extensive expan ion

s s is s and contraction ; the pair of tentacle placed neare t the mouth the stoute t . The

O f is s position the tentacles be t seen from the actinal side (ﬁg. The whole actinal s surface is covered with a plating of lime tone cells , which leave but a small circular f o . Opening, the mouth , in which the points the teeth project This actinal system is

ss o f as circular ; there are no notches for the pa age the gills , in adult Echini the

n s ambulacral tentacles are placed one above the other . The lo g spine move in every

as - - s o f direction , they are already provided with the peculiar ball and ocket j oint Echi

- n o ids. s o f s o f On removing the Spine one Of the e young Sea urchins , the great size

’

n n . 2 7 s the tubercles ( , , ﬁg ) and the large circular actinal sy tem give them an aspect totally different from what we are accustomed to associate with the genus Toxo

2 s s n e u ste s. It . 7 p The teeth ( , ﬁg ) ﬁll but a mall part of the actinal ystem ; they are

s ﬁve narrow triangular wedge , extending from the centre to the edge Of the shell , covered partially by the network o f limestone plates . (See ﬁg . The test th u s

s s O f denuded o f its spine resembles in all the general feature that a Cidaris. With the

o f s exception the formation of the abactinal ystem , which is not yet developed , the — o f - as striking features the young Sea urchin such the circular actinal system , its

s s o f o n e large ize , the great prominence of the tubercles , the po ition the pores above — the other are all characters belonging to a different family from that to which the

- n s - adult Sea urchin belo g . The little Sea urchin does not long retain these anomalous features ; with every day of increasing age the changes which it undergoes bring it

l - f closer and c oser to the condition o f the adult . In a young Sea urchin o a diameter o f o n e f 2 8 ﬁfteenth o an inch (ﬁg . ) the spines have lost almost entirely their embry o n ic n character , the tentacles are much more umerous , and pedicellaria have made 1 2 ON THE EM BR YOLO GY O F ECHINODERMS . their appearance in the interambulacral space they are more thickly scattered than in

o r . s s s s the ambulacral , where there are merely three four The abactinal y tem con i ts of a single large plate coverin g the op ening of the anus (a ) which leads out o n o n e side

f s o it . The additional spines and plate which have been formed are all developed from the abactinal region . The new plates are added in a spiral manner round the anal

s plate by additions to the limestone ma s , pushing further away from the abactinal pole

s o f s is o n the ﬁrst formed plate . The outline the new plate at ﬁrst indicated the lower edge , which becomes somewhat undulated then the transverse divisions are made , and

n s a spine is forme d o the plate soon after that . There are no spines on the la t formed plates ; the spines when they ﬁrst appear have the same fan- shaped character as the

s s . 24 s earliest formed spine Of the abactinal urface (Figs . , Thi shape they lose

s soon , and pass at once into spines resembling the older ones in every re pect except size . The mode of formation o f the new plates w as discovered by Professor Agassiz as

1 834 s o f s early as , when he gave a hort account it in the Edinburgh Philo ophical

is s s Journal . The Spiral arrangement of the plates till very plainly vi ible in adult

- specimens . Although the Sea urchins are circular , we have in their mode o f growth

Of o f something which reminds us the earlier embryonic stages the Starﬁsh . I have n o t b e e n ab le o f - h o . to trace all the various stages of growth the young Sea urchin , w

2 s s s . 8 it pas e from ﬁg to the condition when the pores , in tead of being arranged in

o n e o n s s o f single rows above the other , are placed in arcs both ide a median ambu

lacral . row covered with spines We may , however, form a tolerably accurate idea o f the changes which m u st be gone through by examining the abactinal part o f the

- ambulacral area Of an adult Sea urchin . The mode o f formation o f the ovarian and

- . o f 28 ocular plates remains still to be traced The Oldest the young Sea urchins (ﬁg. ) has advanced sufﬁ ciently to enable u s to see that the subsequent changes which are required to make it agree with its adult condition are by no means as great as the

- h as changes which the young Sea urchin undergone up to the present time . It h as

s u s n To xo n e u ste s reached a condition which assure that we deal with a you g p , and

. . s s so s nothing else The pigment pot , marked in the younger stage , are smaller and

is scattered more uniformly, the muscular band around the mouth well developed , the

h as plate covering the actinal area separated from the edge of the test , and is moved

s by the muscular membrane which cover the actinal system . There are no notches as yet in the actinal part Of the test . The teeth have n o t changed their form from that found in earlier stages (ﬁg . there are from seven to eight tubercles in each verti cal row of the ambulacral and interambulacral zones . I was unable to distinguish ON THE EM B R YOLO GY OF ECHIN O DERMS . among the many tentacles the original Odd tentacle which was so prominent in the

s younger stages . Neither have I succeeded in determining the po ition of the eye in

o f s o f s n - w s any the tages the e you g Sea urchins , o ing to the early pre ence of the spines

- s u s and Of the large pigment cell , which prevent from Obtaining a favorable view of the o dd terminal tentacle in the young forms ; neither have I bee n able to sati sfy myself whether this o dd terminal tentacle retains its original po sition during the whole

- i as s s ﬁ . s sa life Of the Sea urchin , the ca e in the Star sh I can likewi e y nothing con

o f cernin g the development additional ambulacral tentacles .

The ﬁgures Of young Sea- urchins which Miille r has given belong unfortunately nearly

f To xo n e u ste s so all to di ferent suborders from our p , that we cannot make the com

- s as s s parison with our young Sea urchins as clo e we might wish ; and be ides thi , the ﬁgures o f Miille r are not drawn in such a way as to discriminate between the parts

s is which belong to the ambulacral and interambulacral spaces . Thi particularly evi

in h is dent ﬁgures from the mouth side , where we frequently ﬁnd tentacles in such

s o f i f n am u l numbers as mu t make the development the d f e re t b acra unequal . The .

s s o n e W same is the case with the pine . Any who ill take the trouble to compare the

o f - o f o f ﬁgures young Sea urchins Plates IV . and VII . his ﬁrst Memoir , Plate VII .

. s ﬁ s . 2 4 fourth Memoir, and Plate IV eventh Memoir , with the ﬁgures given here ( g

s s will see that, although they agree in their general character , yet it is impos ible to place the different spines o r tentacle s in such po sitions that they will be divided into ambulacral and interambulacral regions , which is easily done with the ﬁgures I have

’

. a Cl e astro ids given We must remember , however , th t most of Muller s ﬁgures are yp ff and S patangoids , which may make it di icult, if not impossible , to divide the young

- W Sea urchin into ambulacral and interambulacral areas , here we have nothing like

to u s as o u r To xo n e u ste s. f h o w regular vertical rows guide , in p One great di ference,

u s is Miille r in ever, will strike at once ; it , that what has called anus I have my

ﬁgures called mouth . The view he has taken is probably due to the fact that the

- young Sea urchin s from which he made his drawings were compres sed . Having fol

in lowed the mouth the different stages which have been represented here , I think ii there can be but little doubt that M lle r was mi staken . Compare ﬁg . 26 Of this

an d h is . 3 . paper with ﬁg , Plate VII ﬁrst Memoir , we cannot fail to come to the con

’ elusion that it is the mouth which is turned towards us in both cases . If Millle r s

- s statement were correct , we should have the anomaly in young Sea urchin of ﬁnding all

l s the tentacles between the spines and the anus on the abactina side Of the te t , while on the actinal area we should have nothing but a clo sed membrane . This is so contrary

Of Starﬁsh e s o r to the plan of development Echinoderms , whether Echinoids , , Ophiurans , 1 4 ON T HE EMBRYOLOGY o r ECHINODERMS .

v o f s th e a from the obser ations Muller him elf, that I give accompanying expl nation , which seems to bring the ﬁgures o f Miille r in accordance with what I have ob served .

’ Miille r s s o n The appearance o f the teeth , in ﬁgure , what seems the abactinal side , is

o - s s Miille r due to compression al so . The spines of the y ung Sea urchin Ob erved by have a very uniform appearance ; they are nearly all hexagonal prisms in their earliest stages .

- s s The same is the case with our young Sea urchin , though they lo e their embryonic

iille r character at an earlier period than is the case in any species ob served by M .

Emb ryologica l classiﬁ ca tion of Ech in oids . From a careful examination o f the different stages through which our youn g Sea

s its to s urchin pa ses during development , and after comparing these stages form resem

o u r s s as bling them which are now found living in ea , we Obtain valuable hints to the f relative standing o f the different families o some Echinoids . We can extend this somewhat to other orders by availing ourselves of th e additional Ob servation s o f Miil

Cl e astro ids ss ler, and of a few facts concerning the development of yp noticed by Profe or

’

s i e n . s ss s m u Aga siz , which will be g y here Profes or Aga iz Observations were ade pon

i in a l o f s s o f M ell ta testucl ta K . so young pecimen , which is common along the whole

f Echi C. a o o ur s N . Southern coa t , from Beaufort , , to Texas ; upon the young st ges n arach n ius arm a G o f o ur p ray , which are found in great quantities in the stomach

En c e o h o Enco e Va lencienn esii . Cods and on the young of an p , probably p Ag The

' se rv atio n s o n o n s M ellita lon ssa Mellita I had occasion to repeat an allied specie , giﬁ

o n s o f Mich . , which is exceedingly numerous the beache in the neighborhood Acapulco ,

Mexico .

s o f s The mallest specimens Mellita observed , mea uring about one seventh of an inch

s s in diameter , are nearly circular ; they have but a ingle lunule placed in the po terior i ‘W interambulacral space ; this is no larger than the prick o f a needle . ith advancing

h as h as age , measuring one ﬁfth Of an inch , its outline not varied much ; the lunule

h as f h e . o t grown larger When it attained a diameter of one third an inch , outline become s slightly indented at the place where the two po sterior ambulacral lunules will eventually be developed . As the posterior interambulacral lunule is n o t homologous

s O s a to the others , but is imply an pening for the anus , we have in the ﬁrst t ges de s a s u s its cribed condition which remind s at once of Ech in arach n ius. It next lo es

‘ h as D e n draste r circular outline , becoming somew at eccentrically elliptical , in ; while

o f s a ra after the formation the two po terior lunules it h s all the a spect o f a Lo b o ph o .

s s o f s As it increases in ize two other indentation are formed , the indication the po ition

Of the two anterior ambulacral lunules . These lunules remain Open for a con siderable period of the growth o f the urchin ; we cannot fail to recognize in this state o f the

O 1 6 O N TH E EMBRYO LO GY OF ECHIN DERMS .

Ech in o c am us n s s Rh a h do cl y lowest ; then the rou ded Clypea ters , Clypea ter and p y y

s s s pus , in which we have the ﬂoor connected by but few upport ; then forms uch

L a an u m th e a s as as g ; then circular Scutell , uch Arachnoides , in which the anus is

Ech in arach n iu s D e n draste r Sca h e ch in us th e supramarginal then , , p ; then genera

L o b o h o ra Ech in o discu s Ech in o l cu s En co e . p , , g y , p , Rotula , and Mellita Adapting in a similar way the ob servation s of the different stages o f our young

s s s Echinus given in this Memoir to the true Echinoids , we hould for imilar rea ons

o f ae D iade m atida place lowest the family Cidarid ; next , the ; then that peculiarly

Ech in o m e trada embryonic family, the , in which the unwinding of the pentagons leaves

- ' - s the Sea urchin with oblique axes then Sea urchins with few larger pines , such as

Ech in idarid H lio cidari d s o c a e a . o f the and In all the e families , with the exception the

H e lio cidarid E h in m e rada a c o t is . and , the ambulacral system particularly simple We

- s s next have those Sea urchins with a more complicated ambulacral y tem , in which the tubercles become numerous and are not arranged in such regular vertical rows as in

Ech in ida To xo n e u ste s an d H i o n o ida the true , p , the like ; then the pp , and the like , in

v s which the de elopment of the ambulacral sy tem reaches its greatest complication ,

s s s in which the spine are exceedingly ﬁne , and in many genera ( uch as Salmaci and Mespilia) resemble more what we ﬁnd in the Clype astro ids ; passin g gradually

‘ as Bo le tia Tri n e u ste s H i o n o e Me s ilia through forms such , p , pp , Salmacis , p , to take

n a their greatest degree of complication , both in the ambulacral and i terambul cral

l n u H o o e ste s. regions , in p The correspondence between th e embryological development and the order of succes

o f so o u t o f to sion Echinoids in geological times is striking, that it may not be place * o f show some o f the principal points o f agreement . The number fossil Echinoids

n as o f know is so great , that , when we have large a number embryonic forms for each

s o f specie to compare with them as are here given for a couple species , we shall not fail to draw most important conclusions for o ur knowledge o f the classiﬁcation o f these animals .

Ech in o ids The earliest , Twhich make their appearance with the Trias , are without

- s n exception Sea urchins , belonging to familie which have emi ently embryonic charac

A S SI Z L . R s é de s Ech ino derm e s . de s . N at 1 8 46 47 . See AG , Catalogue ai onn An Sc ,

I s s s as P ala ch inu s Eo cidaris D T omit intentionally the pre ence of uch form in the Silurian , in the evonian ,

A rch a o cidaris s s s s s and the many and Melonite of the Carboniferou , until a comparative tudy of the e form with the younger stages of Comatula h as been made . I am convinced from what I know of the embryology of

s s s f Echinoderm , that they are only ynthetic and prophetic Crinoid , and have there ore nothing to do with our present subject. N O TH E EMBRYOLOGY o r ECHIN O DERMS . 1 7

id s. Cidar a ter The make their appearance ﬁrst , and the other genera , of which a

s Cidarida th e few repre entatives are found , belong to a family closely allied to the ,

H e m icidarida o f Cidarida , a prophetic and synthetic family combining features the ,

- s D iade matida w . which have preceded them , and of the P eudo , hich are to follow them

E h inolam n c o r . We have not a single Clypeastroid , p , Spatangoid D uri g the Lias the

' Cl e astro ids re re se n ts th e yp make their appearance , but the type which p suborder , the

s Co ll rite s n o t as . genu y , is a Clypeastroid , we understand them in the present epoch It is Cl e astro ids a type which is the forerunner of the true yp , and which apes the char

acte rs . o f of the Spatangoids The Echinoids the Lias have not the strong, embryonic

s as H e mi e din a D iade m o sis character which belonged to the Trias ; we ﬁnd uch genera p , p ,

o f i d m a id D a e a o f o u r . and the like , which remind us forcibly the t present time In the

a s Of s lower st ge the Jurassic period the Echinoid are of still more varied genera , such

H o le ct u s P aste r — s u s a o f as yp and yg , being form which recall to the embryonic st ges

ro i Ech in o lam s s u u our Clype ast ds. The p are likewi e introduced with Pyg r s and Echi n o b rissu s while it is only in the lowest Cretaceous deposits that the ﬁrst Spatangoids

a To a o a o i appear as H o l ste r and x ster. If we c mpare the appearance o f the Clype str ds in geological ages with the embryonic stages Of which I have given a short account , we shall ﬁnd that the ﬁrst true Clyp e astro ids (Clype astro ids such as we know them in o ur o wn Scu te llin a th e time) are such forms as and Lenita , in Eocene ; it is only in the

M o ce n e s its s y that the genus Clypea ter appears and takes greate t development , aecom p an ie d with a large number of true Scutell a ; and it is not till the Pliocene that genera

s n A m h io e En co e M re embli g p p , p , and ﬁnally ellita , make their appearance , showing a closene ss of agreement between the order o f development and the geological succession carried o u t to the fullest possible extent .

I OPH URANS .

To th e extensive investigations of Muller about th e embryology of Ophiurans and

s Holothurians I have but little to add , and I con ider myself very fortunate to have bee n able to increase our knowledge Of two o f the orders Of Echinoderms after what has been done by him . h i Op h iOp o lis bells Lym .

N A m h iura s uamata Two Ophiurans are quite common at ahant ; one , p q Sars ; h i h li b lli O 0 o s e s . the other , p p Lym The latter , unfortunately , does not lay eggs from which the plutean stage is developed , as the young Ophiurans are never nomadic .

s s o f The egg are laid in bunches , from which , according to the observation Professor

as 1 849 O h io h olis Agassiz , made as far back , the young p p is developed , very much 3 VOL . 1 x . 1 8 ON THE EMBRYOLOGY OF ECHINODERMS .

A steracan thion M u lleri th e after the manner Of Of Sars , without passing through plu

o f n s s s tean stage . So many points investigation have arise since tho e ob ervation were

' made that they must nece ssarily be very incomplete without a re n ew e d co m parative

o f s study o f the whole subject . I here copy from the drawings Professor Agas iz two stages o f the young Oph io ph o lis which will enable us to compare the two modes of

s u s as s A ste racan development , and how clearly for Ophiuran as I have shown for

’ o f s s o f thion in the ﬁfth volume Profe sor Agas iz s Contributions, that these two modes 2 development are but longer or shorter ways of arriving at the same point . Fig . 9 is

o f h i lis h o ne o f the more advanced young Op o ph o seen from the abactinal side . At t is stage it shows prominently the arrangement of the abactinal plates and th e po sition o f

- A s A ste racan th io n arm . the joints in young , we have a central plate , and ﬁve radial and ﬁ ve interradial plates . No hooks or granules are as yet developed ; only two Of the

' b e o n d o f ro e ct . tentacles have reached any great development , and p j y the edge the arms A careful examination of the young Ophiura in this stage would enable u s to deter

- . s mine the exact place where new arm joints are added There seems ome doubt , from

* ' s o f Miille r o f Liitk e n as the ob ervations and , 1 to whether the new joints are formed

o f o r . O s Starﬁ sh e s at the base the arms at the extremity From what I have b erved in , it is evident that the n e w parts o f the actinal and abactinal portion o f the arm s are not

s n e w tarﬁ sh e s added at the ame place . The suckers in the S are formed nearest to the

n e w o f o f odd terminal ocular tentacle , while the spines the abactinal side the arm

o f . o . o f are formed at the base the arm (See V l V . of the Contributions Professor

s o f s o f o f the s Agas iz , where a full account the increa e the arms young Starﬁ h will

. a be found ) Something similar may occur in Ophiurid , and would account for the

' diﬂe re n ce o f opinion entertained by Mii lle r at different times as to where the new arm 30 f joints were added . In ﬁg . we have the actinal side o a young Oph io ph olis some

- . 29 as what less advanced than ﬁg ; there are yet no arm joints , and the W hole outline is pentagonal ; two o f the tentacles alone make their way through the actinal lime stone ﬂoor .

m m a a A p h iura squa t Sars .

o f is i The Pluteus which a ﬁgure here given (ﬁg . 3 1 ) s probably the larva o f

A mp h iura squam a ta . I have found these larva only three times during two su m — ﬁ 3 2 s. 33 mers , once in June , once in July , and then, the young Ophiuran ( g and )

o during the ﬁrst week of October . It probably requires as l ng a time as this for the

a development of the Echinoderm , as I have kept the larv which were caught in June

I . U E J . 1 8 48 V. 1 85 2 . M LL R , Memoir , , and Memoir ,

" ' LUTK EN . . A dditam e nta Hi s O h iuridarum . K 1 858 . I , C F ad toriam p jobenhavn , ON 1 THE EMBRYOLOGY OF ECHINODERMS . 9

n and July for weeks without notici g any striking chan ges . These Ophiuran larva resemble very clo sely the Pluteus o f Op h ioth rix fragilis and the P lu teus b im a cula tus

o f s M lle r h is n a a * ii o th e . Trie te , ﬁgured by in Memoir Ophiuran Larv Of the Adri tic il ’ . 3 1 M ll 1 f e r s . o Fig resembles more ﬁg , Plate VII . the Memoir just quoted , than any

other . The order of appearance o f the arms o f thi s Pluteus agrees with his observa

o n o f h ra ilis . O h iot ria: . V tions the younger stages the Pluteus Of p f g (Memoir , Plate

. ﬁ s 8 h as n VI g . This been traced in a specimen considerably you ger than the

’ o n e Miille r s o f P lute us bim acula tus . . 1 figured here , resembling figure (Plate I fig , Me moir with the exception o f the different degree o f development o f the arms C an d

’ D o f f 1 h s e o . 3 . s t e that ﬁgure In this younger Pluteu , arm corresponding to ﬁg were

" ” s e e the longest next the arm , then the arms scarcely projecting from the curve ’” ’ ’ n a as as r joini g e and e . The arms e in the adult larv are twice long the othe s

” " . e e . (fig while the other arms , , , are all nearly equally developed With the o f f n a exception this di ference in the proportion of the arms , the you ger larv did not ' m difle r in the essential parts from the o n e which is figured here . The most co plete histories which Miille r has given us o f the development o f any Echinoderms are those

P luteus bim ac la o f O i ri ra ilis u s n o t Of u tus and p h oth x f g . He gives only the complete

s o f h as hi tory of the changes the larva , but follows the young Ophiuran after it

i s M ller a s t . a i b orbed calcareous framework Here , gain , the ﬁgures of seem to con tradict is h is s s his text ; he says the framework dropped , but ﬁgure how that , on the

is s contrary , nothing lost , that every part of the Pluteus is ab orbed by the Echino

’

. 5 ii . V . . . . M lle r s Of V . derm . See ﬁgures Memoir , Plates IV , , VI , VII , VIII Fig , 3 ﬁ s. 32 3 Plate VII . agrees exactly with the stage represented by me in g , ; the long

’ e ff a its arms are cut O for w nt o f room ; every other arm can be traced , with ex

tre m it s s a o f . y perfect , di appearing gradually into the sub t nce the Ophiuran This

s s f s as Pluteu is quite tran parent , and did it occur in su ﬁcient number it would be ‘favorable a species to follo w the development o f the Echinoderm as the Brachiolaria ﬁ o f o ur Star sh e s.

The greater similarity o f the Ophiuran larva to Echinoid s than to Starﬁsh e s is

o f th e something very peculiar . The same thing we ﬁnd again repeated for two other orders ; the larva o f Holothurians an d o f Starﬁ sh e s resemble each other to a remark

in o f s an d able extent , the character of the arms , the absence rod , the aspect Of the

- s s is . water tubes. In Ophiurans and Echinoid thi resemblance still closer The arms

- o f are supported by rods in both , the water tubes are small , and the general outline

M ceres. Funfte . 1 85 2. U E J . O h iurcn larv e n de s s M LL R , Ueber die p Adriati chen Abhandlung Berlin , 20 ON THE EMBRYOLOGY OF ECHINODERMS .

o n the plutean forms is so similar that they might easily , first examination , be mistaken for larva o f the same orders . a s o f . 31 is All I wish to how from the figure this Pluteus (fig ) th t in Ophiurans , as Starfi sh e s o n well as in Echinoids and in , the Echinoderm is developed the water

s — 6n e tube , (the left) developing the actinal , the other (the right) developing the

— is abactinal region , that the tentacular pentagon Open in the larval condition , and is s o f only closed by a proces unwinding , some time after the actinal and abactinal

s s surfaces have been formed , though this closing take place in Ophiuran and Echi

f ﬁ h e s o n n o ids s O . Star s while the Echinoderm still retains part the framework In ,

s o f the contrary , the clo ing Of the pentagons takes place after the resorption the

- - Brachiolaria . From the position Of the water tubes it is self evident that the loops

o f o f . 31 t o n e th e the pentagon tentacles (ﬁg , ) are not in plane ; they connect with ’ - b - w o f water tube , and we ﬁnd all the essential features Of the tentacular water tube )

. . . . . c . . to n o t the Brachiolaria (See Proc Am Acad , l , ﬁg The tube is connected

‘ ’ - with the tentacular water tube w . It would be interesting to observe whether such a

o f o f o n connection takes place , also the mode formation the ﬁrst limestone particles

- w o f o f s the water tube , as this would facilitate the study the development the ame

o f parts in Echinoids where the opacity the larva prevents accurate Observations .

Miille r o f s has , in nearly all his ﬁgures the Ophiuran plutean form , represented the

- o f two s . water tubes as made up distinct part , having no connection This probably

f - arose from the strong contraction o the water tubes in certain parts . I have noticed in the larva which I observed a marked tendency in the anal portion o f the water- tubes

o ﬂ o f - to contract , and thus apparently to divide from the remainder the water tubes ;

w as f s - this , however, but temporary , and the moment a terward the water tubes had

s as . 3 1 w w . a sumed again their fully expanded shape , in ﬁg , , The young Ophiurans f ﬁ s. 32 33 o s ( g , ) are remarkable for the total absence the plates of the di k ; they are

- ’ not even indicated by the presence of Y shaped limestone rods . The only calcareous

' 3 2 o f s - . s deposits we have (y , y , ﬁg ) are evidently parts the ﬁr t arm joints , the dor al

- 2 s . 3 s . 32 (y , ﬁg ) and side arm shields (y, ﬁg ) of that joint , which con ist at pre ent of ’ . e re but a few rods , indicating their future position The arms are the last to be

” " o f . 32 r s e e sorbed ; in the stage ﬁg they retain their full length ; the other a m , , ,

v as s are in a ery contracted condition , they have been almost entirely re orbed by the

o f two o f young Ophiuran , leaving nothing but the extremities the rods the arms are not entirely resorbed (ﬁg . i s s . 33 This young Oph uran , een from the lower ide , ﬁg , shows that the tentacular

pentagon h as entirely closed . The ambulacral system is similar to the tentacles o f ON THE EMBRYOLOGY OF ECHINODERMS .

s the young Starﬁsh , and must have been formed in a imilar way from the original

f . 1 o 3 . . . . . simple loops ﬁg (See Proc Am Acad , ﬁg Additional tentacles are

’ d o f t m as therefore forme at the base the odd loop , probably in the same anner in

A e ra h io n is f t st can t . o The mouth not limited by the formation the actinal ﬂoor ; his , as as s o f well the abactinal area , is in the present tage almost entirely made up the

s remaining portions of the Pluteus , which have not been re orbed , and through which

f n the parts o the you g Ophiuran are seen . The number of young Ophiurida ob served is not su ﬂi cie n t to enable u s to

u se o f make much their earlier condition for a classiﬁcation . The ﬁgures of the

’ iille r s o f L tk e n o f young given by M , and the few pecies which ii has studied some * o f Kro e r . the earlier forms , together with the observations y , are all we have The

o f A stro h ton e ucnem is . T. Liitk e n A ditam en to ad ﬁgures young p y M , given by in his d

H isto riam O h iuridarum s o f a . p , throw some light on the clas iﬁcation Ophiurid Hav ing had the opportunity to examine very young specimens o f A s trop hyton A gassiz ii

i M e f s S t m . . . o r p , collected at Eastport , by Mr Verrill the Mu eum at Cambridge , I was

h is s s f enabled to repeat ob ervation , and ﬁnd the same remarkable di ferences between

n k s you g and adult which had already been pointed o u t by Lii t en . A young A tro

‘ phyton would seem at ﬁrst glance to belong rather to A ste ro n yx or A ste ro po rpa than to Astrophyton . The disk is circular ; there are no ribs ; the arms have but

On a single fork . The ribs the disk make their appearance when each arm has U divided three times ; that is , when there are twenty terminal points . p to that

d o f w re perio the rounded plates the disk were quite prominent, some hat sembling

i i is s fﬁ in their arrangement those o f the disk o f Oph o ph o l s. This u cient to show th at the A st ro ph ytida stand highes t among Ophiuran s ; that Ophiurans with smooth

s s as O h io l h a A m h iu ra arms , as Ophiura , are lowe t ; next come uch genera p g yp and p ;

O h io h o lis O h io co m a O h io th rix in p p next ; while p , p , and the like , which the spines

s s a take their greate t development , stand highe t among Ophiurid proper. f The stages represented in figs . 32 and 33 are somewhat di ferent from any given ii l s o f . 2 M l e r . . 4 by ; the nearest condition are those fig , Plate VII and fig , Plate IV .

M o f is s fifth emoir , in which the outline the young Ophiuran far le s well defined , but in which the abactinal plates , as well as the arm plates , are further advanced ; i i o f s . ts the condition the tentacles nearly identical In general outline fig . 33 differs

ﬁ . 30 s but little from g , where the abactinal and actinal ﬂoor are more advanced , show ing otherwise no differences which would lead us to suppose that the mode o f develop

KR O Y ER . . Tidsk rift III 1 840 . Nat , , 22 ON THE EMBRYOLOGY o r ECHINODERMS .

ment o f these two forms w as apparently so contrary . Let us take the Pluteus at the

o f a o f its time o f the appearance the young Ophiur n , and deprive it arms , we should soon ﬁnd o u r Pluteus in a condition in which the nomadic and sedentary mode Of

n s s u s h n as development could n o t be disti gui hed ; howing that for Op iura s , well as

arﬁ sh e s s s o f so f for St , the e two mode growth , at ﬁrst di ferent , reach , early in the * o f . development the young , stages which are identical

H OLOTH URIANS .

Cuvieria Fa bricii D ub . e t K o r. In Holothurians the two modes Of development seem to combine in a very remark

h as s a s s able manner . The larva hort arms only in the early st ge it remain nomadic

s fﬁ o f after they have di appeared , when it would be very di cult to tell by which the

’ n M iill r s . e s two modes the you g Holothurians have been developed See ﬁgure , in

’ W alze n fo rm i e o which the Auricularia approaches the g form , f urth Memoir, Plate I . From the young Holothurian s which I have myself observed I am not able to say

w - s o f anything concerning the ater tube , and must therefore make a comparison the

l r Memoirs of Mii le with what has been suggested here . Although we have a Sy

n a ta Ch iro do ta Caudina arena ta Stim . p and a p ) which are very common here , all my

o r a attempts at artiﬁcial fecundation , at ﬁnding their plutean st ges with the other h a . o f Echinoderm larv , ave completely failed The only Holothurian which I have

Cu vie ria is l a Off N seen the young is , which tolerab y abund nt in deep water ahant , and of which the young, in the more advanced stages only , however , are found from

s June to October . The tudy of the development of an Auricularia with reference to

- s the part the water tubes play in this would be particularly intere ting . Holothurians are the only Echinoderms studied by M iille r in which he distinctly

s s says that the young Holothurian re orb the whole of the pupa, as he calls the

o f s n envelope the Holothurian , and which lo e nothi g during the development . On

s s s o f o account of this re orption , he con ider the plan the H lothurian development to

s f be something special . I tru t I have made it su ﬁciently clear that resorption takes

' The fact that Oph io ph olis lays its eggs in bunches seems to lessen the diﬁ ere n ce between the Echinoderms

s s s s s s which lay egg and tho e which are viviparou , or retain the egg in bunche in a ort Of pouch at the base of

s as . 34 s s s A ste racan th io n A . Jlf ulleri the anu , in ﬁg , which ﬁgure how the manner in which a mall , allied to

s s its s s Of . s is Sar , retain egg till they have reached a very advanced tage development Thi ﬁgure borrowed

s m ss ss 1 848 . I O s s th e s s s from drawing ade for Profe or Aga iz in n the phiuran , al o, young of ome pecie are retained in the body of the parent till they reach a very advanced condition . "uatrefages h as Observed thi s.

ss ss D r. s s S s s . L Profe or Aga iz and Simp on have al o noticed it in a pecie from Charle ton , and Mr Theodore y

K i n s it as . s an d . 1 8 2 5 . man ob erved on the co t of France See al o Schultze rohn Mull Arch . for 5 and 1 8 7

O ON THE EMBRYOLOGY F ECHINODERMS .

1 s n f . o way through the envelope , When compre sed , the mode of branchi g the young tentacles is clearly seen .

n as o f s I complete these Observations are , they are con iderable value in a zoological

‘ s t point of v iew. It is evident that tho e Holo hurians which want the ambulacral t e n tacle s " and s s ﬁ have only a limited number of tentacle round the mouth , uch

s s are as Caudina , Synapta , Fi tularia (the Apode ), in which there but very few

s s s as depo its of lime tone particles , tand lower than those Holothurians in which ,

Cu vie ria Pso lus in and , some of the ambulacra are provided with suckers , forming \ a o f s s kind sole , and in which the lime tone particle perform an important part in

s covering the body . We should therefore place higher still those Holothurian in

as n which , in the precedi g group , the tentacles round the mouth have a highly ram iﬁ e d s o n character , and which have be ides ambulacral suckers equally developed

‘ f o f the s s the di ferent ambulacra . It is evident from this that several form Ob erved

‘ n Pe n tacta s Pso lin u s . by Forbes ,1 uch as , etc , will prove to be only the you g Of , sinc e he has distinguished genera principally from . the degree of development Of

i O the g lls and f the ambulacral system .

V GEN ER A L PL A N OF D E ELOP MENT .

The figures Of Muller show without doubt that in Holothurians as well as Echi n o i n is s s ds the you g Echinoderm in its earlie t tage s an open spiral star . An exam — - in a i n s fi s. . fi s t o . 6 9 . 5 8 of the figure of Plates III g , V g , and Plate VI . first Memoir,

f s . 1 4 s 4 I o . . fi . 6 7 9 X . . 3 4 l and Plate VI fig , VII g , , , , and figs , , fourth Memoir , wil satisfy any o n e that h is figures cannot be made to agree with o n e another o n any other supposition than that of an open pentagonal spiral surface which develop s the actinal

o f o n f o f o n e - o f s s system Echinoids the sur ace water tube , and a similar piral urface on

’ - s M lle r s the other water tube which develop the abactinal area . In the same way ii

s o f o ﬁgures Of Auricularia , particularly tho e Plate I . fourth Mem ir , and Plate III .

s m m s sixth Memoir, how that the young Holothurian also co ence by having an open

s o f A u ricularian s spiral actinal tentacular ystem . The ﬁgures young which are given

. s w s b on Plate I fourth Memoir al o show without doubt that the tube hich lead to , in

M i - . 36 o f s s n s to ﬁg thi emoir, the tube leadi g from the water tube the dorsal pore , and

is M ll r b . ii e s that really the madreporic body al o considers it as such in his ﬁgures ,

' r h as ir e n o f and it is certainly ve y remarkable that , with the admirable ﬁgures he g the young Ophiuran and Auricularian , he should not have noticed the intimate con n e ctio n o f - o f is n a the water tubes and the young Echinoderms . It atural th t the

L . A S SIZ . s . 1 8 63 . O B E S . Hi s s S tarﬁsh es. AG Method of Study T F R , E A tory of the Briti h ON THE EMBRYOLOGY OF ECHINODERMS . 25

idea which he entertained , that we had in Echinoderms a passage from the bilateral

as h is to the radiated form , should have made such a strong impression to prevent

Of as noticing the radiated character the young embryo , hidden it is by all this external appearance o f bilateral symmetry . And had it not been for the clear idea we have

’ now O f the character Of the part s o f radiated animal s" I doubt not that Muller s view

s would have gained general acceptance among investigator , and the whole frame

o f ss s f work cla iﬁcation , ba ed upon the idea that a plan pervades the di ferent types

Of the animal kingdom , would have fallen to the ground , if it could have been clearly proven that in Echinoderms we had a transition from o n e Of these plans to another . A s embryology gives u s the means o f distinguishin g o n broad principles th e class o f s h as s Batrachian from that of the true Reptiles , since it been hown conclusively by

' s ss ss Profes or Aga iz that the Batrachians are an eminently embryonic cla , while the

O f Reptiles proper are a synthetic type , so the embryology Echinoderms throws a h lig t o n the character of the orders which compose that class . Particularly important is this knowledge when applied to those early form s which have been

s s as Starﬁ sh e s o r s con idered by some geologi ts , Echinoids , Ophiuran , thus placing

f s m s o f the ﬁrst appearance O these order far back in geological times . A co pari on

s Of o u r Starﬁ sh e s - s the e types with the embryonic forms , Sea urchin , and Ophiurans , will show u s plainly that they have nothing in common with them . The few fea

s as ture which have misled investigators , and have prevented their recognition true

o r . Crinoids , are either synthetic prophetic characters Crinoids are an eminently

Of th e s synthetic and prophetic type . From the time earlie t appearance Of Crinoids

s o f Starﬁ sh e s the characters which they combined fore hadowed the advent the true ,

s . so the Ophiuran , and the Echinoids The synthetic characters were prominently

o f Starﬁ sh e s o r - developed that many them are readily mistaken for Sea urchins , for the same reasons which have made it so difﬁcult to recognize as true Reptiles those synthetic forms in which Fish or Batrachian features concealed the true Reptilian character , until we had obtained a reliable guide in the distinctions pointed out by w embryology . If these views are correct , the Crinoids are the only Echinoderms hich

Pala o z o ic is n o t are found in the period , and it until the Secondary that the other orders appear.

arﬁsh s as The St e an order are characterized by the absence of prophetic features .

arem b r o n ic They are rather a p y order ; that is , certain features which are character

. H . th e . S . s. I II I . L A S SI Z . s s . AG Contribution to the Nat i t of U , Vol , V 4 VOL. 1 x . ON TH E O o r 2 6 EMBRYOL GY ECHINODERMS . istic o f the embryos Of Echinoderms are carried to a great prominence in the different families . These are , to give a few examples , the great development Of the marginal

o f o n s plates the arms , the character of the spines the abactinal area , and the pre ence Of ﬁ Star sh e s. o n pointed tentacles in the adult Ophiurans , the contrary , are a peculiarly

s in embryonic order . They never develop interambulacral plate , which , as we shall see * A ste racan th io n s . , develop quite late in the life Of the young Starﬁ h What is very remarkable in all the young Echinoderms is their Crinoidal character . A stem added to o r o f a very young Starﬁsh , Ophiuran , Echinoid recalls to us many the forms with

ala o n to lo ical which we are familiar in the p g history Of our earth , and I have no doubt that a comparative study Of the innumerable Crinoids known , and Of the living and

Starﬁsh e s o ut Of fossil Echinoids , , and Ophiurans , will bring many more points interest

o f than have been here alluded to , and give us a correct idea , not only of the nature f ' O . the orders , but also the families which compose them I have here pointed out a

' fe w o f the characters which distinguish the diﬂe ren t orders Of Echinoderms ; I shall

o f endeavor to adopt the same method , to show how far what we know the embryology Of Echinoderms will assist us in formin g a true conception Of the classiﬁcation Of

Radiates , reserving closer comparisons between the development Of Acalephs and Echi n o de rm s th an for another occasion , when I shall treat more fully I have room for here

o f a u s Of the development the Ctenophor , which gives the connecting link between

. Ca le n terata the Polypoidal and Echinodermal mode Of development The division of ,

Le u ck art s s proposed by in contradi tinction to Echinoderms , does not corre pond to any natural distinction we can draw between the mode Of development of Echinoderms on

o n e o n . the side, and that Of Polyps and Acalephs the other The mode Of develop

o f diﬂe rs s — a ment Polyps more from that of the higher Acaleph the Ctenophor , for — f instance than that Of the Ctenophora di fers from the Echinoderms . But what is a fatal Objection to the division proposed by Le u ck art is the appearance at th e earliest

o f o f o f s h e ro m e re s d stages development deﬁnite numbers p , whether we eal with a

s h e ro m e re s Polyp , an Acaleph , or an Echinoderm ; and these p are not simply analo

s as o f s gou parts , the tentacles the embryos of ome Annelids and the arms of the

o f s h o m o lo o ris plutean state Echinoderms , but are trictly g , showing plainly that

s s the same plan underlies the mode Of development Of these three cla se , though it is f carried out in such di ferent ways in Polyps , Acalephs , and Echinoderms , and that

s o f s the eparation of the great type Radiates into two branches , as propo ed by

Le u ck art s h as n o , is an artiﬁcial divi ion which true foundation in nature .

. . . . H s . . . L . S ss . See Vol V of Contrib Nat i t U , by Aga iz ON THE EMBRYOLOGY OF ECHINODERMS . 27

EX PLANATION OF THE FIGU RES .

W TH ﬁ I x Of s. 29 30 34 s b v . the e ception g , , and , which were copied from drawing made Mr Tappan , under

i ss ss s s s the d rection of Profe or Aga iz, the ﬁgure were drawn on wood by my elf from the drawing I made at

s the time of thi investigation .

TOX OPN EUSTES D ROBA CHI ENSI S A G .

— FIG S . 1 28 . — — s 1 1 s fi s. 1 9 27 The pecimens from figs. 8 inclu ive were all obtained from artificial fecundation ; g were

- w s . caught ith the dip net ; ﬁg . 28 was thrown up on the beach after a torm

EX PLA NA TION OF LETTERIN G.

" ” a s. r e . , anu , rod of arm b i s s. , madreporic body . ndependent rod above oe ophagu

" c s . r Of s th e O s. , alimentary canal (inte tine) , anal point ofjunction rod in phiuran Pluteu d s s . s . , dige tive cavity ( tomach) actinal region

’ ” ” ’ " e e e s Of . 3 s s s e e s s. , , , arm the plutean form , pot of arm , of the Pluteu of Echinu

" b rach io lar s s s i s . f , arm s interambulacral pine of Ech nu

s s Cuv ie ria. s s s s. g, tentacle round actino tome in younger pine of Echinu ’ a s Cuv ie ria . t s. g , ambulacral tent cle of , tentacle

' h Of s. t Odd t . , teeth young Echinu , terminal ten acle 1 Cu v ie ria . v . , body of larva of (pupa of Muller) , anal part of vibratile chord

’ m . v . , mouth , oral portion of vibratile chord ” n s s. v s. , interambulacral tubercle of Echinu , vibratile epaulette

’ - n s. w . , ambulacral tubercle , water tube

' - o o s s. w m , e ophagu , water tube leading to adreporic body .

- . O . pedicellaria y, terminal arm plate of phiuran

’ - r . s s O . , abactinal region y , ide arm plate of phiuran

’ ’ s s s . I . 3 1 0 s v v ice v e sa . r , main rod , formed ﬁr t in the Echinu Pluteu n ﬁg hould be , and r

i s s ﬁ s. 1 5 . A m . . s s s For the earl er tage compare g of Proc Acad , from which the earlier tage of the Echinu

Pluteu s do not differ greatly .

- . 1 . Fig Proﬁle view of an Echinu s Pluteus eighty eight hours after artiﬁcial fecundation .

2 . s . 1 . as s . Fig The ame ﬁg , een from above

. 3 . w s . 1 s d is Fig Proﬁle vie of a plutean form omewhat more advanced than in ﬁg ; the dige tive cavity, ,

s bent very con iderably towards the actinal side .

. 4. s s d is s f Fig View from above of a Pluteu in which the dige tive cavity, , omewhat di erentiated by con O ON THE EMBRYOLOGY OF ECHIN DERMS .

’ s s 0 i x i h as s Off i w w rs triction ; the pouch , , formed at the bl nd e trem ty, ent two d verticula, , ; the ﬁ t

- appearance Of th e water tubes. End of fourth day .

. 5 . Of an s . 4 Fig Profile view embryo omewhat more advanced than fig , at the beginning of the fifth day ;

’ s c s d s s 0 well s — w s s s the inte tine, , tomach, , and oe ophagu , , are eparated ; the water tube, , al o tand out

x o s s o Of v s prominently from the e tremity of the e ophagu , the anal part vibratile chord, , bulge out

considerably.

- . 6 is s s h as . Fig a view, from the mouth ide, of the tage the embryo attained at the end of the ﬁfth day The ' - s w w iff s ss s oeso h water tube , , , have d erent degree of development, and are le clo ely connected with the p

s s s ss s s s v . agu the rod have ent out proce e at point where the new arm are to be developed, at

7 is . 6 x t s s s . 2 s a view of ﬁg from the anal e tremi y, to how the change of form ince ﬁg , and the po ition of

the vibratile chord .

. 8 is . 6 m is O . Fig a proﬁle view of ﬁg the mouth , , not yet pened

. 9 . s m is Fig A proﬁle view of an embryo taken at the beginning of the eventh day ; the mouth , , opened ;

’ - th e w s s s . s s h s s water tube, , reache nearly the dor al urface The current which previou ly to t i tage had

a as as o s carried the food through the only opening, , far , and then were reversed to eject the dige ted

m ss s s in s d matter, now come in through the mouth, , pa through the oe ophagu , rotate about the tomach , ,

- ss ﬁ rst O a s a is s n . and pa out through the formed pening, the nu , which hereafter u ed o ly to eject the food

1 0 s s s s s as s repre ent a Pluteu at the beginning of the eighth day, een in uch a manner to how the whole

k s s . of the vibratile chord, when loo ing on the ide where the mouth and anu open

s s in . 1 0 1 1 is a proﬁle view of an embryo lightly more advanced than the one repre ented ﬁg .

1 s s . . 1 2 . s as . 1 g The ame ﬁg , een from the mouth ide

2 as 1 3 . . 1 s so s s h as n r Fig . Somewhat more advanced than ﬁg , een to how the change the vibratile chord u de

1 0 . gone sin ce the stage represented in ﬁg .

in s s ’" 1 4. s s a s e e Fig . An embryo during the tenth day, een proﬁle how the po ition of the rm and

’ 4 s s e 1 5 . s as . 1 s Fig . The ame ﬁg , een from the mouth ide ; the arm , , have been greatly developed ; the

ff s c s d s s o is . s di erentiation of the inte tine, , the tomach , , and oe ophagu , , quite complete Fir t appearance ” - s v . s s s of the vibratile epaulette , The water tube have not united they have not greatly increa ed in ize.

” - e h as its i 1 6 . s r Fig. Proﬁle view during the twenty third day ; the arm, , made appearance, and al eady i quite promin ent a still greater development of the vibratile epaulettes s perceived .

1 6 s s th e i iff s 1 7 . s as . as Fig . The ame ﬁg , een from above, to how relat on of the d erent rod to each other,

t. well as the ﬁrst appearance of the tentacular loop,

s ss s a s ﬁ s. 1 0 1 3 s 1 8 . . 1 7 Fig . View of ﬁg , corre ponding to the le advanced t ge of g and , howing the connec

tion of the different parts of the vibratile chord .

. 1 7 s s n 1 9 . s s Fig. A much more advanced tage than ﬁg , een from above found wimmi g freely on the urface

s x s u s s s s s of the water . The rod e tending into the arm are made p of three et of rod united by hort tran

- verse bars ; additional tentacular loops have been formed . The water tubes have greatly increas ed in

. size, and appear to have united

s Toxo neustes dro bachiensis in i - i has i 0 . A n e x Fig . 2 adult Pluteu of p , wh ch the young Sea urch n already O ON THE EM BRYOL GY OF ECHINODERMS . 29

cro ach e d somewhat on the an al e xtremity . The Spine s are q uite prominent ; the vibratile epaulettes

' ' ’ " s s s s s s e e is s s have acq uired a very large ize two very prominent pot , , , in the arm , , f perhap ome f thing homologou s to the brachiolarian arms O Brachiolaria .

. 2 1 . . 20 s ﬁ s. 1 0 1 3 1 8 . Fig View of ﬁg , corre ponding to g , , and

. 0 . Fig. 2 2 . Proﬁle view of ﬁg 2

. 23. s h as s s h as Fig The young Echinu materially encroached on the Pluteu , and re orption been carried on

s x is x to uch an e tent that there very little left of the Pluteu s e cept the arms, which have lost their

mobility .

. 2 4. s fte s s s n s . Fig A young Echinu immediately a r the re orption of the Pluteu , een from the abacti al ide

- 25 . Y s . 2 4 s s . oung Sea urchin omewhat more advanced than that of ﬁg , een from the abactinal ide The

O the s a . 28 s s s is pening of anu ( , ﬁg ) cannot be traced in the e younger pecimen , though it very apparent

in somewhat more advanced ones.

. 2 6. s as . 2 5 s s s s s s g The ame ﬁg , een from the actinal ide ; the tentacle have become more lender ; the pine

more numerous than in younger stages. The actinal membrane is well developed .

. 27 . s as ﬁ s. 25 2 6 s its S s s s . 0 The ame g and , tripped of pine , een from the actinal ide

in . 28 is To xo ne uste s s a a young p mea uring one ﬁfteenth of an inch in diameter, cluding the length of the

S s l s s ss pine , in which pedice laria have developed, and the pine have a umed the general appearance of

those of the adult .

OPHIOP HOLI S BELLI S m x.

I S . 29 30 . F G ,

. 29 . i O h io h o lis s w n s th e s . g Abactinal v ew of a young p p , to ho the arra gement of the plate of di k

li 29 s s . . 30 . s O h io h o s . Fig A omewhat younger p p than ﬁg , een from the actinal ide

I R A A MP H U A S"UAMATA S R S . — 3 1 33 . FIGS .

- A m h iura s a s . . 3 1 . s is Fig An adult Pluteu of p , in which the water tube are pl inly een The ﬁgure taken on

’ m a s is off . I s v is v the side of the dreporic body ; one of the long arm cut n thi ﬁgure the anal, and the

oral vibratile chord .

’ 32 . s s s s x s e s Fig . The arm of the Pluteu are almo t entirely re orbed, e cept the two long arm , , which are till

s . O is s i as . 3 1 ntact, in ﬁg they are here cut off for want of pace The phiuran een from the abactinal

’ - S s s . ide, to how the arrangement of the arm plate , y, y

' 3 2 s s . h is s l s t t 33 . s as . Fig . The ame ﬁg , een from the actinal ide The mout til very large the tentacle , , ,

mere loops.

A STERA CA NTH ION F LACCI D A A G .

° f s A steracan thio n accida . 4. O . 3 Mode carrying the embryo in ﬂ g 302 o N TH E o r N R ’ EMBRYOLOGY ECHI ODE MS .

ET K R . CUVI ERIA FABR I CII D U B . O — 35 38 . FIGS .

ieria O s s th e m o nth d . . s uv P g 35 Y ounge t C b erved, in which the tentacle of o not yet protrude beyond th e

general outline of the pupa.

ie ri . 5 . 36. Cuv a 3 s . Fig A much more advanced than ﬁg the tentacle , g, are very prominent

Cuv ieria s f 6 . 37 . s O i s . A m Fig A till more advanced , in which the po ition the madrepor c body , , can be een

’ b ulacral s s . tentacle , g , have al o been formed

. 38 . Cuv ie ria in s . 37 ss S the dff e n Fig A young nearly the tate of ﬁg , compre ed to how the relation of i er t

p arts to each other .