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OPHIURA BREVI SPINA. SAY,

A DISSERTATION SUBMITTED TO TIE BOARD OF

UNIVERSITY STUDIES OF THE JOHNS HOPKINS UNIVERSITY

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY.

BY

CASWELL GRAVE,

BALTIMORE , 1300

^•r/7

CONTENTS .

1. Introduction. X.

2. Historical Sketch. £•

3. Distribution and fjfcits. 7.

4. Physiological Notes. 11

5. Early Stages. /6,

G. Stage "A". Origin of Anterior Enterocoels. If,

7. " "B". " " Hydrocoele XL

3. " "C" Closing Of the Blastopore and Formation

of the Mouth. M'

9. " '^"Rotation of the Hydrocoele completed .-

10. " "E" .Second Pair Tentacles. 30,

11. " "F" .Invagination of the Nervous System. — 3?.

12. " "©".Degeneration in LArval Organ Begun.— ipjt

13. " "H" .Formation of Subneural Sinus. ^

14. Elation of Larva to Adult. 4|T.

15. Larvae of Antedon and Ophiura Compsr--i . <<>X-

1C . Literature Cited. •©<<>.

17. Description of Figures. t /»

io. Vitt. 13.

— INTRODUCTION—

During the Summer of 1838 it was jay privilege to occupy
the- Hopkins table in the U.S.F.C. laboratory atVWoods Holl
' ile here I rediscovered the peculiar Ophiuran larva
which v:se first found and figur:cl by KROKN ( ).

Finding the larvae he described in the open sea KROKN lid
not know to what species they belonged, but the larvae/,the
development of which is the subject of the greater part of
this paper, came from eggs laid in aquaria by Ophiura
brevispina. It is not likely that the same species of
Ophiuran occurs both at Funchal , where KROHN did his work,
and also at North Falmouth, where my material was obtained,
but it is very probable that species belonging to the
C-enus Ophiura have similar larval forms.

Among Eehinoderms where a direct development from the
larva to adult occurs, that is: without the usual highly
specialized intermediate pelagic larva, we usually have
to do with a species which in some manner takes care of
ite brood, but in 0. brevispina the larvae are free-swim-
ming, they being provided with a well developed locomotor
apparatus, yet the usual Ophiurid pluteus larva is as com-
pletely omitted as it is from the life history of the vi-
viparous Amphiura squamata.

From the fact that the usual pluteus skeleton is begun
in the larvae of D. brevispina one ie lei to suspect. that
at some period in its history, the species possessed a

more nearly like e pluteus than at the present

tine. On the other hand on account of the resemblances
which exist between the larva or O.brevispina and
Antedon rosacea( treated of in another place )v;e nay
suppose a close phylogenetic relationship exists be-
tween them, If?as many zoologists believe, the crinoids
have retained more nearly than any, other group the char-
acters or the primative echinoderm stock, then in the
Ibrvc of O.brevispina we^have on: which has retains!
unmodified its primative characteristics.

But these considerations are foreign to the sub- -
ject natter of this paper in which the facts only of
development are treated.

Tile method used in the preparation of the material
for nlcrcscopical stuay and which gave good results is
as follows: -The larvae were taken up into a pipet with
as little water possitl; and squirted into a snail
bottle containing a solution of sublimate-acetic^
(98 parts sat .sol.IIgCl^ being used to 2 parts glacial
acetic acid). After fron two to five minutes the sub-
limate solution was drawn off gently leaving the larvae
at the bottom where they had settled. Then 50^> alcohol
was added which in a few minutes v.'as drawn off and re-
placed by 10% alcohol in which a little iodin had been

dissolved . In a few hours this was changed for cle^r

. muddi

75Jb alcohol in which the larvae remained until p^sriy.

for laboratory study. After staining lightly in acid
carmine. so as to facilitate their orientation ,ths larvae
?/ere dehydrated in the usual way and cleared in oil of
cloves . From the clove oil they were oriented by a mod-
ification or the PATTON method. After an impregnation
with 55° paraffin, series of setions three microns in
thickness were made in three planes , transverse (long-
itudinal sagittal and longitudinal horrisontal. The
sections were stained on the slide with KLEINENBERGS
haematoxylon. Other methods were tried but none proved
so satisfactory as the one just described. The shrink-
age in sehinoderm tissue, which usually accompanies the
unmodified paraffin method ^was not to be seen in the
tissues of thifese larvae due, no doubt, to their unusual
thickness.

It has been thought best to make the following
list of terms which are used synonymously in the text
of this paper in the description of the larvae. Those
in the same line can, in most, cases , be interchangably
used.

Dorsal , — aboral , — above , — over .

Ventral , — oral , — below , — under .

Anterior, — forward, — before.

Posterior , — backward, — behind .
In the drawings of the larvae, when the ventral side is

up and the anterior end is nearest the- top of the page,
then the readers left is also left in the figure.

For convenience in description, the various stages
taken to illustrate the life history of the species
have been designated by letters of the alphabet; this
method seeming preferable to one in which age is used
as a distinguishing character, since the progress of
development at any ace depends so intimately on the
varying conditions of environment.

I take this opportunity to acknowledge m$ indebt-
edness to Dr.C.P.Sigerfoos at whose suggestion I began
the study of Ophiuran development.

I was aided very materially while at the Fish Com-
mission laboratory by Prof .H.C.Bumpus who placed at my
disposal every facility for work at his command and to
him also I am greatly indebted for many suggestions in
methods of rearing larvae at the sea-shor* .

To Prof. Brooks, under whose direction my, work

o/yu

has been done, is due my warmest thanks for the inter-
est with which ho has followed me in my studies and
^rr the many valuable suggestions he has offered from
time to time during the year.

HISTORICAL SKETCH.

The species of Ophiuran,Ophiura brevispina ,the
life history of which is the subject of this disserta-
tion , was first discovered and described by Thomas
Say in 1325. (//•)

Since this tine the species has been rediscover-
ed and renamed as many as three tines. It is probabiy
best known at &%e present friing- by one of its synonyms,
Ophiura olivacea , which was given to it in 13C5 by
Theodore Lyman (f.) . In his earlier work LYMAN distin-
guished 0. olivacea and O.brevispina but in his Chal-
lenger report on the Ophiuridae and Astrophytidae ($) .
he places the two species together as one under its
earlier name e ich, although less descriptive of. .the
species than that given by LYMAN, it is probably best
to retain.

In 13521 AYERS described the species under the
name Ophiodema olivaceum in Vol. IV. of the Proc.Bost.
Soc .Nat .Hist .

LUTKEN also described it as Ophiodema serpens
in 135G.

DISTRIBUTION and HABITS.

Ophiura brevispina is a very widelgt distributed
species it having been reported from points along
the Atlantic coast from Brazil to New England.

It has been taken from the bellowing localities.
( l).Bahia , Brazil . (2) .Port Antonio , Jamaica .
(3) .StThomas , Bahamas . (4) .CapeFlorida, Florida.
(5) Tortugas, (G) .Beaufort ,NorthCarolina.

(7) .OldPointComf ort ,Va . ( 0) .CagHartor ,NewYork .
(0) .Dartmouth. (10) .NewBedford,Mass.
(11) .North Falmouth, Mass.

That »art. of North Falmouth "arbor which .*ke

A

max »art. o

scecies inhffbit-3

species inhabits is very shallow, its depth at low
tide not exceeding one fathom.

The bottom is covered with a mat of living and
lead grasses and algse and in this tangle, together
with a great variety of crustaceans ,mollusks arid
wo rms , the opiiu rans 1 ive .

The usual color of the species is; an olive green
with darker bands on the arms and,. clouded dish.

A

Through the blending of their colors with the

fim. fjalUMnam

sea-weed tke$r are greatly protected from their en-
emies and it is «*** difficult when looking for them

''A

to see them e.monc the sea-weed go long as they do
not move.

It is quite- conmon to find a srx.ll Amphipod
crustacean, ( ), clinging to the arms

of dredged specimens and from the structure of the
crustacean it is probable that the two species live
t oge t h e r c omme n dtl 1 y .

What benefit either animal can derive from
the association is difficult to see.

A

One pair of the thoracic lego of the crustacean
is so modified as to form a structure ideally adapted
for clinging to the round ophiuran arms. The last
segment but one of each of this pair of legs is /Y*^.
shaped .At the end of one arm of the /Y'V is attached
a movable segment ,the end segment of the leg, which
when shut down upon the end of the other arm of the
><Y*r encloses a triangular space in which the ophiuran
arm in held.

The body of the crustacean is colored and band-
ed in such a manner as to simulate closely the color
and banding of the ophiuran arms.

When placed in aquaria with their host ,th
crustaceans cling to the ophiuran arms until the
water becomes depleted of oxygen, when they leave the
arms and swim about the edge of the dish apparently
much alarmed.

From an examination of the contents of the stom-
achs of several ophiurans one is led to suspect
that the creatures are scavengers^since it is quite
common to find bits of other animals such as a crus-
tacean appendage &. None were ever observed to eat
anything when kept in the laboratory and it is quite
out of the question to observe them in their natural
habitat since they arc nocturnal animals remaining
hidden during the day.

Ths ophiurans were first examined for sexual
elements early in June and at that time the ec^s
were very large but adhered closely together in the
gonads. The sperm appeared to be fully formed but
were nonmmtile .

From this time on Until the middle of August
the species was regularly watched and examined and
on July 16". ths first ripe eggs and sperm were ob-
tained. A great number of specimens had that day
been dredged and placed in aquaria dishes of fresh
filtered sea-water. One week later a great number
of adults wepe again brought in and placed under the
sane conditions as those which had spawned in the
laboratory the week before, but this time very few

eggs were obtained and all subsequent tor get the

A

ophiurans to spsvm were unsuceesful.

From this it would seem that the breeding sea-

son is extremely short.

The tine of day at which spawning occured cor-
rcspor.dc well with the time at which I have noted
it to take place in Ophiophilus aculeata and Ophic-
coma echinata,that is, between 3 and 10 Cfclock P.M.

PHYSIOLOGICAL NOTES.

The- locomotor movements of an ophiurid, upon
a casual observation, seem to consist of an uncoor-
dinated writhing and twisting not calculated to bring
the creature to rood or a place of safety except by-
chance; but a more careful study shows them to be
the result of an orderly and nicely coordinated mech-
anism.

The rapid strides which characterize the move-
ments of a brittle-star are in strong contrast with
the slow creeping movements of a star-fish ot sea-
urchin, the difference being due to the employment
of different locomotor mechanisms in the two cases;
the star-fish and sea-urchin depending entirely upon
their tube feet and spines while in the ophiurids
the arms them selves are the efficient locomotor
organs, they being used much as we use our arms in
swimming .

The arm of an ophiurid consists of a large num-
ber of segments each of whiGh contains a central
calcarious ossicle. The calcarious ossicles of ad-
jacent segments articulat; with each other li'.ce the

e

vertebra^ of the spinal columnand are joined together

by two pairs of muscles in such a manner that motion

is possible 'in all directions. This mechanism is
aided in producing the locomotion of the creature <

not only by the arm spines where they are present
but by the Toot tentaclesi.TheseTlatter organs, which
are the homologu.es of the tube feet or other echini
oderms,have been previously regarded as having given
up their locomotor function entirely but I shall show
further on that this is not true in the genus OPhiura

The experiments I carried on last Summer on the
movements of ophiurans resulted in little that is
new, but oh account of the confirmation my notes and
photographs give to PREYERS work ( ) on the same
subject ,it has been thought advisable to publish
them.

ot?t/ The usual method of progression ha for one arm
4rd precedent taking no other part apparently than
to point out the way • the two arms adjacent to and
behind the anterior arm make the stroke, the remain-
ing arms are dragged behind acting as a rudder .Fig. 1.

No preference as to which arm should prec
could be found in an adult ophiuran each arm being
equally capable of going before , making the stroke
or following behind.

If greater speed is needed, for example, to get

sway from a strong stimulus, the arm which precedes

may also take part in the stroke, fts contractions

fep&*made simultaneously with those of the side arms.

This added force if produced repeatedly on one side

would soon chans-:- the cours^of progression but this

difficulty is overcome by an alternation of the

stroke of the preceding arm, first on one side then

on the other. T><J. 1.

In s third method of normal locomotion the arms

are arranged as in Fig. 5 . in which only one arm

follows acting cs the rudder .This leaves twc pairs

of arms for the stroke but the anterior pair Is

usually meet vigorous in Hi contractions.

Since no physiological differentiation into

anterior, posterior or lateral parts is to be found
in ophiurids the creatures are under no necessity
of turning fche body when a change in the direction
of progression is to be made; the arm which finds it-
self pointing in the new direction to be traveled
takes the lead although it may have been either lat-
eral or posterior in position in the previous movements.
As has been mentioned before- the foot tentacles

aid in making the strokes of the arms efficient in
propelling the body. After a stroke has been made ,
while the arms are being drawn forward and extended

actively about, but as the arms coins to rest Tor the
backward movement, the tentacles are thrust down a-
gainst the substratum and cease to move. The tenta-
cles tentacles thus fit themselves into the inequal —

ities of the surface and fe4**s afford fixed points
to pull against. THe tentacles or the posterior arms
act in the same way and are efficient in preventing
the force of the stroke being lost in side motion.

In ophiurans with long arm spines these latter
structures may perform the function just described
for the foot tentacles , but in the genus Ophiura the
arm cpir.es are very minute and closely applied to
the sides of the arms.

It is interesting to note. the wonderfull coor-
dination of locomotor movements immediately follow-
ing the amputation of throe of the arms .In this
case if the nerve ring has been uninjured one of the
remaining arms takes up the part of guiding and bal-
ancing while other strokes first on one side then on
the other. F/<J$ 3.a**L¥,

When the central nerve ring is cut at any point
coordination in movement is impaired and when cut in
five places , between the arms, it is lost entirely.

Bhen placed en its aboral surface an ophiuran
quickly turns over. The method used is quits definite

tv:o adjacent arms straighten ou$ so that Ithey/togethor)
form a straight line . On thess arms as an axis the
body revolves being pushed over by the three remain-
in-? arms but mostly by the median one of the three.

EARLY STAGES.

The mature eggo -re opaque and vsry in color
from an olive green to an orange yellow. Those or
the same-Mndividual hoisrever are constant in their
coloration. Until quite well developed the larvae
retain the color which wao on the eggs at the tine
they were laid.

For echinoderms the eggs are very large ,being
.3 mm. in diameter.

Soon after they are fertilized the eggs throw
off two membranes the first of which is much thicker
than th? second .

When first laid and. their early development the

A

eggs float, but when their cilia are formed the larvae
arc able to swim below the surface.

Not knowing that any special interest would be
found in the life history of the species the earliest
stages were not carefully observed while living nor
was material preserved for future study;and,as I .
hove stated elsewhere, all laterattempts te jet other
material were unsuccessful.

This makes it necessary to begin this paper
with the description of a late gastrula in which
the first pair of enterocoeles have already begun
to form 8 0 lateral pouches from the anterior free

end of the archenteron.

Larvae in this stag= or development will b«
designated as "A".

STAGE A. 3C Hours old.
At the age or thirty siz hours the larvae, swim
actively, they being uniformly covered with cilia

Fig.l.

The shape of the larvae is an oval, the length
being to the shorter diameter as 2 is to 1.

The animal or anterior pole is sleightly
pointed than the posterior vegitative one. The ven-
tral surface is distinguished by the presence of the
blastopore v:hich latter has been pushed from its
posterior position to a ventral one by the rapi ■
growth of the sctoderm of the dorsal surface of the
larva. .

An apical plate of taller cells is present at
the anterior snd but I could not see that the cilia
at this point were any longer than those which cover
the other part- of the larva, "ty. 3. *£

From ths blastopore , through which its cavity
opens to the exterior, a large archenteron projects

j.rd into the blastccoele.

The remainder of the blastocoele ,not taken up
by the archenteron or its pouches, is filled with a
close net-work of mesenchyme cells. This mesenchyme
tissue is shown in Fig, 3, which is a longitudinal
sagittal section of "A",

From the anterior Tree- end of the archenteron
a large pouch is in process or being cut off .This
pouch projects to the right and left as horn like
processes which latter are to be considered &a the
rudiments &£ frho rudimsnta or the right and left
anterior entsrocoeles.Fig.2. wi *-*- oudL.

As to the method of gastrulation I can not at
present speak from observation on larvae in which it
is just taking place but from a study of the stage
now under consideration, some idea can be gotten
as to how it has proceeded. In Figs.l and 3. we see a
cellular plug nrotruding from the blastopore and also
extending far into the archenteric cavity. In some
cases it extends even into the enterocoele pouch.
The contour of this cellular mass is ragged &e is
also true of both the outer and inner surfaces of
the wallof the archenteron and the inner surfs ce of
the rctezierre.

These facts seem to indicate that gastrulation
does not take place by invagination, as is usual in
echinoderms.but that the larva before gastrulation
is a solid, planula like, affair, and later the arch-
enteron is formed by a splitting away of the central

core. In the same way the plu~ or colls is formed,
by the hollowing out of ths solid archenteros..

Besido their ragged outline- the walls of ths
larva!- have another peculiarity in their structure,
forjudging by the number and position of the nuclei,
they are from two to thro-:- colls in thickness ,E!ig. 3.

Cell walls arc- not to be mod: out in any stags
of development .

STAGE "B". 42 BDURS.

According to BURY(2) .the hydrocoele does not
have the sams origin in all the groups of echinoderms:
he found that it originates in the crinoids , sea-
urchins and star-fishes from the left antorftor ent-
erocoele but in the ophiurids it grows out from the
anterior end of the left posterior enterccoele .

This observation which BURY records with appar-
ent hesitation, I can completely confirm as will be
seen in the description and figures of "B" .

Externally the appearance is the same as in
"A" but the internal structures have undergone a
great change.

The anterior pouches, the cavities of which
in aA" were connected both with each other and with
the cavity of the archenteron,are now separate and
distinct. The connection between these structures
still continues however in their fused walls. She
left pouch is a little larger than the right and
lies behind and to the left of the latter; fu if asJi.

Just below the anterior' pouches there is to

be found a third pouch which is growing out from the

left side and anterior end of the archenteron. It

UMA.

protrudes anteriorly and partially the two anterior

enterocoeles .Fig,4.hy. The cavity of this pouch,
which is the rudiment or the hydrocoele, is in wide
communication with the archenteron.

From the wall forming the convex side of the
hydrocoele there are, even at this early stage in
its formation, five outgrowths which arc th-s begin-
iiigs of radial canals of the adult ophiuran.Fig,4,
1,2,3,4 and 5 .

The whole hydrocoele is curbing round to the
right to encircle the oesophagus which latter is mak-
ing its first appearance in this stage as a shallow
but definite pit in the central part of the ventral
ectodermal wall .Fig ,4, oe .

To avoid confusion the hydrocoele was spoken
of above as arising from the archenteron but, as will
be seen in th? transverse section(Fig,5,)tafcen in a
plane posterior to the origin of the hydrocoele, a
differentiation is taxing place in the archenteeon
which enables us to distinguish in it the- rudiments
of two structures, the posterior enterocoeles and
the stomach. By a longitudinal circular furrow the
archenteron is being cut horrizontally into a large
ventral pouch, the posterior enterocoeles, pe. , and
a smaller dorsal one, the stomach, s. This stomach

rudiment bends around the posterior end of the post-
erior enterocoelo pouch and opens to the exterior
through the blastopore ,Fig,4,b,

It is from the left side and anterior end or
the ventral pouch that the hydrocoele grows out hence
the confirmation of BURYS statement that it arises
from the left posterior anterocoele in ophiurids.

In most echinoderms the postc-rior enteroeoeles
originate as paired structures and if the statements
of BURY and HcBRIDS ar: correctAthat the left post-
erior enterocoelo or the larva forms the hypogastric

. cavity of the adult and the right posterior
enterocoelo goes to form the epigastric coelom"^:
then, according to this, the largs ventral pouch
which I regard as the fused right ana left poster-
ior enteroeoeles ^really represents the left only be-
cause it takes no part in the formation of the epi-
gastric body cavity of the adult ophiurid but does
pass directly into the hypogastric.

The origin oi1 the epigastric enterocoelo is
discussed in the description of "C" in which stage
its rudiment is first found over" the stomach.

lily reason for the 'ventral pouch of "B" as the

A

fused right and left posterior enteroeoeles is that

at the tima of its origin it is symmetrically dis-
posed on either side of the piano of larval bilateral
symmetry.

GOTO (£*) has shown that the hypogastric entero-
coele in the ctar-fishes is not formed from the left
alone byt in it are to be found the left and the
greater yor% of the right posterior enterocoeles.

The cellular plug , which in "A" fills the arch-
enteric cavity, becomes divided by the furrow which
separates the archenteron into enterocoele and stom-
ach and a part of it becomes enclosed in the cav-
ities of :ach of these structures. Fi2»5 CP«

3TAGE "C"
>rm or the

embryos is six hours older than "B'L has
been changed by the appearance of two lateral thick-
enings of the ectoderm a little posterior to the
median transverse- plane. Fig.G.

The blastopore , which in "B"was open to the
exterior ,has closed leaving no trace of its former
position.

The mouth arid oesophagus. which existed in "3"
only as a shallow ectodremal pit ,now have the form
of a deep hollow tube^ which projects vertically in-
ward until it passes through the hydrocoele and be-
yond the posterior enterocoele,when it curves back
under the latter to fuse withthe anterior wall of
the stomach .

Wh-iis The stomach and posterior enterocoelo
are still in open communication .as in "B" .the fur-
row in "C" has deepened and the process by which
the two structures are being separated is almost
c ompl e te . Fig ,7 .

Although the walls of the oesophagus and stomach
are fused, their cavities are sjill separate.

This condition renders it easy to sec- what part
is played by the ectoderm in the formation of the

aliment cry canal, the entire oesophageal cavity being
surrounded b^r ectoderm.

In "B" the hydrocoele communicates with the
posterior enterocoele by a wide opening and at the
sane point in "C" the two structures are still in
in communi cation, but the connection has been narrow-
ed down to a small tube .Fig 7./jc, .

Beside this connection with the posterior ent-
erocoele, a second tube has been formed joining the
left anterior enterocoele with the hydrocoele .Fig. 7. si
This new tube, which is the rudiment qS; the stone
canal, enters the hydrocoele at the same point with
the tube connecting the latter with the posterior
enterocoele .

The left anterior enterocoele lies to the left
of the oesophagus and dorsal to the left half of the
hydrocoele. Fig. 6 a: 7. aol .

It is to be noted that, although we now have a
larva possessing both hydrocoele and stone canal,
there has be?n as yet no pore canal formed. This is
a marked reversal in the sequence of the formation
of these structures from what might be expect 3d from
the order of their appearence in other known echin-
oderms; the pore canal arising usually before the for-
mation of the hydrocoele, while the stone canal appears
much later than either.

Returning to the hydrocoele we rind it a horse-
Figs. 6 and 7.hy,
shoe shaped structure astride the os ;..The '

bulging areas which are to form the radial canals
of the adult, are much longer and more regalar in size
than in "B" . The radial pouch which lies to the right
of the oesophagus and at the 5nd of the right horn
of the horse-she; will here after be spoken of as
radial canal 1. since it arises from that part of the
hydrocoele which was first to bud out from the post-
erior =nterocoele .The other radial canals, passing
to the left over the oesophagus ,will be designated
as 2.3.4 and 5. Radial canal 5 lies in this stage
over the opening of the stone canal.

The rotation of the hydrocoele around the oe-
sophagus from its original left position ^which was
begun in "Byhas continued to such an extent in "C"
that half of it lies to the right of; the median sag-
ittal plane of the larva and half to the left .Radial
canal 3. lies in this plane and pointd directly toward
the anterior end of the larva. n<j. g.

With its rotation the hydrocoele also moves
bodily toward the posterior end of the larva carry-
ing with it the oesophagus . The- oesophagus y coming
in contact with the anterior Wall of the united post-

orlop e'nteraooel-ss , causes the latter to be pushed
in at the point of contact. AS the process continues
those pants of the posterior interocoelej lying on

either side of this inpushing area are forced to
flow forvrard around the oesophagus and under the
hydrocoele : thus we have the posterior enterocoeles
becoming horse-shoe shaped the two horns of which
lie undep the horns of the hydrocoele.

Lying dorsal to the stomach we find a small
enterocoele which was not present in "B%or if present
not in this position. It is the rudiment of the body
cavity which in the adult lies aboral to the stomach
and which has been recently appropriately termed the
epigastric enterocoele. ffo 6 «» 7. -tc.

As to the origin of this structure I have no
direct observation to give but certain facts have

led me to believe that it is fofmed from the right

anterior enterocoele. These facts may be summed up

as follows: In "B" no epigastric enterocoele exists

oja. r cut

but the two anterior enterocoeles (Fig. 4.) lie side
by side, anterior to the stomach and the posterior
enterocoele. In "C" (Figs .6 and7 .)an epigastric pouch,
equal in size to the right antecior enterocoele of "B" ,
is to be found ,but by the side of the oesophagus
only the left anterior enterocoele remains. i|js 6*7 **^

During the six hours which intervene - between
"3" and "C" it seems hardly possible that a complete
formation of the epigastric enterocoele [should
taken place or that there should have been time fof
the complete degeneration and disappearance of the
right anterior pouch} Sufficient time may have elapsed
however for the migration of the right anterior ent-
erocoele to a position behind the stomach.

A - nst such an interpretation as the above

there is the fact that in noAcase has the epigastric

enterocoele been observed to take its origin from

the right anterior pouch. It has been described as

arising from the ri^ht posterior enterocoele however
, 04 JU&4 Xx4Mi, ruhj*J~~h> bcfiu. ,

Ain all the groups by BURY and his observations have

been corroberated by both McBRIDS and GOTO in the

star-fishes .

dTAGZ "D" . CO HOURS.
The chare:- which have taken place in "C" to
produce "D" ar2 very narked.

The cilia have disappeared except in four trans-
verse rings, three ef which axtend entirely around

of the larva. The third ring, counting from
the anterior end, is interrupted by the mout-fr — &«d
oral disk on the ventral surface.

This third ciliated ring first appears or. V. :
lateral bulges which were described in "C",and the
fourth ring appears on a second pair of lateral bul-
ges which originate behind the first pair near t
posterior end of the larva*..

The shape o2 the larva. -is no longer oval but
the posterior end has widened latterally and become
somewhat dorso-ve-ntrally compressed. Fig ,0. The anter-
ior end has not changed in shape and may be spoken
of as forming the handle of the club shaped larva.

Tile enlarged posterior end of the larva contains
all its organs and is the part which will enter di-
rectly into the formation of the adult ophiurid.
From its homology with the preoral lobe and
larval organ of Asterjna gibbosa i have called the
anterior end of the larva the larval organ. It dio-

appears with the metamorphosis into the adult form.

The larval organ is also homologous with the
stall: of Antedon although in the pphiurid larva it
never functions as an attachment organ. When swimming
the larval organ precedes. It is filled with a net-
work of mesenchyme cells.

Internally the changes have- been even greater
than the external ones we have- just considered for
it is during this period of development that the
rotation and readjustment of organs takes place which
ic present in all echinoderms at come stage of their
development.

The hydrocoele, which had begun its rotation
about the oesophagus as an axis in "C" , has complet-
ed it in "D" and reached its definitive position.
That part of the hydrocoele which ,in "C" ,was sit-
uated on the left of the plane dividing the larva
into bilaterally symmetrical halves now lies on the
right side of the same plane, and vice- versa. Compare
Figs.G and 9.

A revolution of 100 degrees has taken place
in the hydrocoele since "C" to which if the 100 de-
grees of rotation be added which too': place up to
the time of "C" we have a total rotation of 360 de-

grees in the hydrocoele. Radial pouch (l)finallyi
after having paseed round the oesophagus, comas to
rest at the point where it originated. Radial canal
(5) ,it will bo noted, is carried only hair as far as
radial canal (l),or from its. point of origin on the
left, to a point opposite on the right of the oesoph-
agus. Compare Figs.C and 9.

This great amount of rotation seemed so pe-
culiar that I hesitated for seme time to believe it
and supposed instead that while the hydrocoele moved
to the right, the other organs lying above it rotat-
ed an equal amount to the left.

The early closure of the blastopore and the
central position of the mouth in the early stages
make such a view as the latter seem possible and as
it may suggest itself to those who study Figs.C and
7, I will give below the points which seem to me,
directly of indirectly, to prove that the hydrocoele
revolves under the enteroeoeles and stomach rather
than that the latter twists over the hydrocoele.

a) .The ectodermal bulges, nearer the posterior
end in "C" Fig,C. are the same as those nearer the
posterior end of "D" Fig.O. on which the third cil-
iated band is situated.

b) .If the latter view is the correct one then

radial canal 3. points toward the same end of the

the larva in both "C" and "D'J Figs. G and 9., but

in "C" the end toward which it points is anteriorly

directed in swimming and in "D" it points away from

the end which precedes. It is hardly thinkable that

at any stage in its development, the anterior end

of a larva should chance its physiological function

and become the posterior end.

c).3y any other view than the one I have adopt-
atiluo \i*^ j&jaa* V*- <uu& ,

ed jthe blastopores ,c t it-' n^ginfil pnsUrJr&fswould

be anterior and the larval organ would be posterior
in position. In all known echinodem larvae the bias-
topore marks the posterior end of the larvae and in
all cases where it occurs the larval organ origin-
ates from the anterior end.

d) ,It may be recalled, as having en indirect
b-er-r^r; eri **-■ qu -'--'• ir>h , that in the readjustment
of parts which takes place during the metamorphosis
of other c-chinoderm larvae the rotation is almost
entirely confined to the hydrocoele .

As the hydrocoele passes round the oesophagus
the tube connecting it with the left horn ef the
hypogastric enterocoele becomes broken and the left

anterior enterocoele together with the tube connect-
in- it with the left horn of the hydrocoele are car-
ried anteriorly round the oesophagus. Fig.O.ael. and
st. In "D" then^we find the stone canal on the right
side of a line dividing the larva into symmetrical
halves Instead of to the left of the sane line as
it is in "C" . Compare Figs.C. and 7. with 9. The
anterior enterocoele stops immediately in front of
fche stomach and oesophagus.

From the point v/here the stone cs.nal enter s\he
anterior enterocoele the pore canal grows out, passes

fuse, and an opening breaks through, the water pore.
Fig.9. and ll.pc. Thus in this stage the eoelom and
hydrocoele are first connected with the exterior.

In "C" the circular water canal had not closed
but existed in the form of a horse-shoe , the concave
side of which opened posteriorly; but as the rota-
tion of the hydrocoele takes place its horns grow
toward each other until they meet. A fusion of their
walls then takes place at the point of contact and
a complete ring is thus formed. The part of the
ring canal, the formation or which hao just been
described, lies between radial canals l.and 5. in

Eig.9. The opening of the stone ©analinto the water

rins is situated in "C" at the base of radial canal
5. but, by means of the rotation cf the hydrocoele
about the oesophagus together with the growth of
the ends of the horse-shoe, this opening is carried
away from its position at the base of radial canal
5. toward radial canal 1. It always remains however
nearer the former than the latter; in other words,
it comes to lie definitively in the ri-^ht edradius
Between radial canals 5. and 1. Compare Figs.G. and 9,

The radial canals, which existed in "C" as sim-
ple pouches from the convex side of the hydroeoele,
have in"D" each become three lobed. Near the tip
and from -the sides of each canal a pair cf pouches
has budded out each of which is about equal in sizo
to the end of the canal which lies between and be-
yond them .Fig.O.et,. and tl. In these three struct-
ures we have the rudiments of the end tentacle and
first pair of foot tentacles of the ophiurid arm.

When we were last considering the hypogastric
enterocoele it was in the form of a crescent , the
horns of which wex?e very short and its central part
ve?v wide. Into its concavity, which was anteriorly

directed, the oesophagus fitted. The horns or this
enterocoele , beginning in "C" to grow over the hydro-
eoele, continue the proceso during the rotation of
the latter, the- horns or the crescent growing at the
expense cf the thickness or its central part , and
in "D" we have t&is enterocoele lying directly over
the hydrocoele in the form of a perfect horse-shoe.
Fig 9. he.

In the concavity of ^.o hypogaoVr-io -jiite-rooeols
is te h- f^rr1 tnn p^^rr-r-l1, . PT_Jn.'ii.

Between the ends of the horns of the hypogas-
tric coelom lies the anterior enterocoele, The walls
of these structures come together and fuse in such
a way that they together form a hollow circular
coelom surrounding the stomach and lying over the
some what smaller water vascular ring. Fig .9.

In the four interradii narked by their positions
between radial canals l.and 2., 2. and 3 . ,3 ,and4 .and
4. and 5. four pouches of the hypogastric entero-
coele grow downward, outside the water vascular ring,
forcing themselves betv/een the radial canals; a fifth
pouch similar to these is formed from the left an-
terior enterocoele in the remaining interradius be-

tween radial canals 5. and 1. Figs .9.12,13, and 14.
hip, 1-2 ,2-3, 3-4 ,4-5, and ipax.5-1. These five pouches
are the rudiments cf the outer perihaemal ring which
will be more fully considered in the succeding stages.

The stomach after being entirely cut off from
the hypogastric enterocoele v.ras drawn forward during
the rotation of the hydroeoele and the oesophagus
was carried in the opposite direction so that in
"B" the stomach lie- almost directly over the oe-
sophagus .Figs .9. and 13. oe, and s. The partition,
which in"C" separated the cavities of these tv.ro
structures, has disappeared in "B" and the oesopha-
geal cavity opens into that cf the stomach .There
is present then in "B" the definitive alimentary ca-
nal cf the adult ophiurid.

The1 cellular mass', which in "B"and "C" was heing
divided into two parte by the constriction separat-
ing the archenteron into enterocoele and stomach,
is to be found.in sections of "D" in the cavities
of both the above structures .Figs .11 ,12, 13, and 14, cp.

Lying immediately above, or aboral to, the stom-
ach, lies the epigastric enterocoele. It has enlarg-
ed considerbly during the interval between "C" and "B"

but is not yet of sufficient size for its fcfeils to
touch those of the hypogastric coelom and hence in
this stage no circular aboral mesentery is to be

found.

STAGE "E". 00 HOURS.

The thickening of the ventral ectoderm which
was begun in "D" has continued luring the si:: houhs
which intervene between "D" and "E" and has spread
tc the sides or the larva, Figs. 15. and 10-21.

r the edge of this thickened oral disk arc-
to be found five groups of rounded elevations of
the ectoderm. The three elevations, of which each
group consists, form the angles of an isoceles tri-
angle .the apex of which points away from the mouth
of the larva. Fig. 15. These elevations^ or evagin-
ated papsllae^lie immediately below and enclose the
tips of those branches of the radial water canals
which form the rudiments of the end tentacle and
first pair of foot tentacles of each arm .Figs 10.
and 21. In this way each tentacle grows into its
ectoderm, the latter closing around it as it pushes
out.

The function of these tentacles in the adult
being mainly a sensory one, it is interesting to
note that they receive their ectoderm from part of
the same thickened oral area v/hich gives rise later
to the adult nervous system.

The ciliated bands in "E" do not differ in ap-

pearance and position from those in"D" but sine:- they
were not figured in the aarlier stage it may be well
to refer to then again in connection with Figs. 15.
and 16. cb 1,2,3 and 4. The first of most anterior
band surrounds the larval organ quite near its tip.

Near the first band and parallel to it runs the
second one also around the larval organ. The third
ciliated band is separated from the second by a
much wider space than that which separates the
• first and second bands. Were it not interrupted
on the oral dish, the third ciliated band would
lie in the line separating the bivium and trivium;
that is, between arms 1 and 2, on the one side and
4 and 5 on the other. The fourth band, passing just.
posterior to the group of ectodermal elevations ly-
ing under the branches of the third radial water
tube, surrounds the posterior end of the larva. _ ,
In "S" the cavities of the oasophagus^have bo-
come obliterate! and the two structures appear in
section as one solid mass of cells .Fig. 20. st and oe .
No degeneration in their size however is to ofesorv-
ed and their outer walls remain well defined, the
oesophagus retaining its connection with the octo-

derm. As will be seen later, their lunen reappear
and they become the definitive alimentary organs
of the adult ophiurid.

Returning to the consideration of the water
system we find in "E", instead of one pair of ten-
tacles on each radial canal as in "D", there two pairs
present; Fig.17.tl and t2. the second pair having
grown out of the radial canal between the first pair
and the water ring. The second pair is much small-
er than those which were fifst to be formed, and con-
trary to what on© would expect, this discrepancy
in size does not disappear as time goes on. This

is also true in the sea-urchins in which the pri-

in the larva
inary tube feet are enormously larger than those
A

which are subsequently formed. The primary tube feet
in this case gradually diminish in size after the
adult form is reached. .

As a rule among eehinoderms the tube feet or
tentacles are formed centrifunally from the radial
canals; that is, between the end tentacle and thelast
pair of tube feet or tentacles Slready formed. This
process keeps the undifferentiated growing point

or each arm at its tip, but in thin ophiuran,and the
same is truo of Antedon,the formation of the tenta-
cles begins in a centripetal manner; that is, the
second pair of tentacles appears, not between the
end tentacle and first pair but, between the first
pair and the ring canal.

This second pair of tentacles is the rudiment
of the buccal tentacles and although differing in
function and position in the adult from that of the
foot tentacles is never the lass entlrly homologous
with the latter. This homology is shown by their
origin and the fact that for a time after forming
they are directed away from the mouth toward the
end of the arm just as ia the case with the foot
tentaeles. After a time however, as will be seen
later, they turn bock and point toward the mouth
thus showing that in this second pair of outgrowths
from the radial canals we have to do with the first
pair of buccal tentacles of the adult: After buding
as ivo see from ths radial canals they migrate to a
position on the ring canal with which we find them
connected in the adult.

In "E" the buccal tentacles have no ectodermal LtoOf

nor rudiment of such, the ectoderm under their tips
being as yet undifferentiated from the oral disk.

The hypoga .trie enteroccele has assumed a more
pentagonal shape than in "D" , it having grown out
over the radial water canals. These projections )f
the hypogastric enteroccele till continue to grow
with the growth of the arr.s and become the brachial
extensions of the body coelome.

The interradial pouches of the hypogastric en-
terocosle , which were beginiag to form in "D" ,have
pushed down further and further between the radial
canals until, coming in contact with the ventral
ectoderm, they bend over inserting themselves be-
tween the ring canal and the oral disk .Figs. 17-21.
hip ,1-2,2-3,3-4 and 4-5. In the same way the pouch
frn- tv jmr'n from the anterior enterccoele has
grown under the water rins in the stone canal inter-
radius. In theesc .f ive interradial onterocoelic eut-
growths,as has been mentioned before, we have the
rudiments of the outer psrihaemal sinus of the adult.
The process by which this perihaemal sinus is form-
ed in Ophiura brevispina agrees in every detail with
its method of origin in Asterina sibbosa as describ-

ed by MeBRIDE (0).

Too epigastric entorocoole is in much the sane
condition as that in which we left it in "D"it be-
ing as yet too snail to meet ana form a mesentery
with the dorsal edges of the hypogastric coolome.
Fig. 10.ee.

The stone and pore- canals tfco have changed very
little during ths interval between "D" and "E" .From
the ring cans! at a point to the left of th« ooijin
cf radial canal l.the stone canal passes upward and
opens into the right postero-dorsal part of the ant-
erior enterocoele. The pore canal begins s^, pni.rtt
at the sane point where the stone canal ends, the
two canals thus having a eommon opening into the"
anterior enterocoele or ampulla. The pore canal ex-
tends from the anterior enterocoele to the dorsal
surface cf the larva where it empties through, tl
dorsal pore at a point a little to the right of the
median sagittal plane. These two canals ,althe
extending in the same direction, do not lie in the
same straight line the pore canal being set a little
anterior to and to the right, of the stone canal.
Figs. 17, 18 and 21. st and pc.Gee also Fig. 11.

STAGE "F". 5. DAYS.

Although "?" is separated from the stage last
described by a, considerable space of tine, the chan-
ges in the larva which have boon brought about are
aasy to follow.

The larva is eonsiderbly larger than in "E"
and has reached itd full development. From this time
on the larval" or-^an gradually degenerates and io
finally completely absorbed by the developing star.
Compare #i:i3.22 and 31. Io.

Th2 external form of the larva has been chang-
ed by the appearenee of a number of elevations and
depressions in its outer surface: the ciliated bands
being elevated upon circular ridges ,Fig"i22,cb 1,2,
3 and4., while at points on -the sides of the disk
beyond the end tentacles, projections in the ectoderm

nade their appearenee, these being the rudiments
of the ophiuran arms .Fig. 22.1 ,11 ,111 ,IVand V.

The larval organ is cylindrical but the disk
has continued its dor so-ventral flattening. Compare
Figs, 22. and 2G .

The first ana second ciliated bands are sit-
uated in the same places as in "E" . T^ie third while

retaining its old position, has grown in upon the
ventral 3isk toward the mouth. Fig22.cb 3. On the

ventral side of the larva tho fourth band has shift-
ed from its 'old positio; behind the third radial
canal to one on the interradii between arms II and
III, and III and IV. It has also become interrupted
on the oral dish in a manner similar to the third
ciliated band. Fig. 22. cb 4.

The depressions, before refered to, are caused
by the invagination of the nervous system which
structure has been forming since "D"in the thicken-
ed oral dish of ectoderm. Immediately below' the water
ring and radial water canals, the thickening 'has in-
creased more rapidly than at ether points *,thus pro-
ducing a ring shaped ridge fro™ which extend five
re.di^l thickened ridges. These rudiments of the
nerve ring anc radial nerves bulge inwardly, no ev-
idence of their presence being apparent en the out-

. When the thickening process has been complet-
ed, tl ■ system gradually sinks in ,

circular groove from which 4rfes five radial
grooves pass out. This is the stage in the formation
of the nervous system which has been reached in "F".

Fig. 22. eg and rg. Th: inv n process begins
at the ends or the / . 3 just inside I

: tips or the end tentacles, the nerve ring

; invaginated loot or all. Co~p-;oe Fiejs. 23-S7.
As development ~o?s on the edges of too grooves grad-
olcse ovfr the nerves, the closure taking place
in too same order as invagination proceeded; that is,,
first over the ends of the radial nerves then fin-
ally, after gradually travelling op the radial nerves,
closing ov:r the nerve ring.

By the meeting and subsequent fusion of too
edges of the grooves, part of their cavity becomes
cut off from th; exterior and io left below the :
ous system as th; subneural space. But Ohio will bo
refered to again i: -r larva in which the pro-
cess of ios formation is mere nearly completed, it

•on in a few only of the r need
larvae of stage "F" ,

The nervous system shows a differentiation
into two distinct layers, a fibrous one nearest the
water system, and a cellular one lying below the
fibers. Figs. 23-20. The nuclei of the cellular lay-
er arc oval with their lone; diameter perpendicular
to the fibrous layer.

Above the nervous system separating it from th:

water system is to be found ths outer perihaemaZ
Ti'qts i-i~io opr.

space. VRe calling the condition of the parihaemal

A

system in Stage "E" we eee that the :-nds of the in-
terradial projections from the hypogastric and an-
terior snterocoeles have grown out over the nervous
system spreading in both directions until the out-
growths of each interradial pouch meet those of its
adjacent fellows in the radii over the origins of
the radial nerves; here the ends of the pouches
fuse and together they grow out over the radial
nerves as the radial perihaemal sinuses.

In star-fishes where the formation of this per-
ihaemal system has been observed, it is said that
no fusion tahes place between the diverticulae of
the hypogastric and anterior enteroeoele interrad-
ial pouches when they meet in the radii, but that a
mesentery is formed at the points where the diver-
ticulae come in contact. This mesentery is describ-
ed as continuing to the :ni of the arm separating
the radial spaces into two parallel cavities.

Nowhffre could I find ouch a mesentery in sect-
ions of the larvae of 0.brevispina,nor could I feel

sure that it exists in the adult ophiuran.

MgBRIDE (9) and GOTO (5))both agree that in
star-fishes the inner perihaemal ring sinus arises
from the anterior enterocoele although they differ
as to the method of its formation. In none of the fawn,
I hav-? is the structure ih question fully formed
but in stage "F" a cavity is originating fas an out-
grov/th from the anterior enterocoele in the stone
canal interradius:, which I take to be the rudiment
of the inner perihaemal ring space. It lies to the
left of the -tone canal near the median sagittal
plan: of the larva. From the posterior silo of the
ventral end of the anterior enterocoele the outgrowth
takes its origin, then extending posteriorly until
past the water ring, it bends over and grows down
until its end reaches the nerve rine; at a point in-
side the outer perihaemal sinus. Here the end of the
pouch in question begins to spread under the nerve
rin~ in both directions, parallel to the outer peri-
haemal ring.Figs, 24 and 2S . ips. This coincides ex-
actly v.'it' its method of origin in Asterina gibbosa
as described by MeBRIDE.

Although the outer perihaemal ring is entir

cut off from the body cavities in this stage there
still remain traces of the interradial pouch:-.- which
::-.-: rise- tc it .FIG.29.hip 1-2, and 4-5.

The hypogastric snterdGC-eie itself has changed
very little since stage "E" but the epigastric has
-has enlarged to such an extent that its edges now
meet the edges of the hypogastric and a circular
aboral mesentery is formed. Figs. 23-29. cm.

In the water system considerable growth is to t-
noted in the tentacles; the end, and first pair of
foot tentacles being capable of protrusion consid-
erably beyond the disk. By means of these tentacles
the larvae are able to cling tenaciously to the sur-
faces or foreign bodies, it requiring a strong jet
of water fre:r: & pipet to detach thorn. Special no-
tice was taken to be sure that it was the tentacles
and not the larval organ whiGh was used so a means
or attachment.

The second pair of tentacles, ( buccal tentacles)
have acquired their ectoderm in this stage and pro-
trude,like the other tentacles, over the radial nerves
into the radial grooves. Fig, 22. and 2G.t2.

The axial sinus or ampulla is present in "F"

it being that pafct of the anterior enterocoele which
remains after the pouches have been out off which
will form the inner perihaemal and pert of the outer
perihiemal systems .Figs 24,25 and 2G.ax sin.

It villi bo noted that beside the ampulla, which
is situated anteriorly to the stone canal, there are
two other fcavities near the stone canal to be ac-
ccunted for .Fig, °C.(sin a)andfsin b) . I car. not
be sure or their origin but I believe they also come
from the anterior enteroeoele. I have distinguished
the™ by the letters (a) and (b) as they are probably
the same cavities as those so lettered by MeBRIDE (0)
in his figures of Amphiura.

The cavity ho has lettered (b'^sn: which he
thinks represents the pi-:ht hydrococle,I have been
unable to find in any of my sections.

The stomach and oesophagus are in a condition
the same so we found in "E" ; that is, without lumen.

STAGS "G" 5, 1/2 DAYS.

Larvae a few hours older than "F" show a de-
cided degeneration in the larval organ, Fig 31. lo.
but other wise the external j-ppocronce of the two
stages is about the same.

The grooves caused by the invagination of
nervous system have begun to disappear by the grow-
ing together of their edges and instead of the deep
furrows we find a sleightly depressed line where
the edges of the grooves have met. Fig.28.rg.

In the norvcue system a pair of tentacle nerves
has been formed from each radial nerve. Fig.31.nl.
They grow out laterally from the radial nerves at
points proximal to the first pair of foot tentacles
around which they grow and to which they belong.

A

ho nerves have as yet appeared to supply the buccal
tentacles.

In "F" the buccal tentacles had only begun to
eurve away from the end of the arm but in "G" this
proximal bending has continued until they curve over
the nerve ring and point toward the mouth .

Beside, this change in the water vascular sys-
tem, we find in "G" the first appearence of the rud-
iments of the polian vesicles. They are four in nun-

bar and are in the form of small inter radial pouches
growing distally from the convex wall or the water
ring. Figs. 31 and 32 pv .There- is no polian vesicle

present, in this species. in the stone canal interradius.

since "F"
££ no pereeptable change lias taken place in the

A

orgsns not revered to above, the description of

?iven in the previous chapter will serve e-
qually as well for "G" as for "F" , and the figures
of these organs in "G" may be examined in connect-
ion with their description in "F" .

STAGE "I?' 3 DAYS.

In the oldest larvae I have, the metamorphosis
das ^eori almost completed. The larval organ has i
ly ^isapp? ,' rt of it s be-

ins found sticking to the -al dish

or ths young pentagonal st r.

When living the little ophiurido elung to the
bottom and sides of the aquari . .. tgh
the ciliated bands were still evident oh the dish
their frcs swimming habits bed been wholly ;ivon up.

The. pore canal still opens on the aboral sur-
face but with the growth of the latter it is tr -
eling toward the 3dge of the lis!: and by a continu-
ation of this process the oral surface will ultim-
ately be reach I.

As the closure of the gr ~ r the nerv=
ous syst::a toed place circular areas below the tips

= tentac] n, the tentacle pores,

and through these the tentacles were able to protrude
ves.

The subneural sinuses wl icl - n to be
fsr:asd in "F" have been completed in the sight
larva .Figs. 31 and 34. ss. In "H" then the nervous

system is cushioned below by the subneural sinus

bove by the cuter perihaemal ring.

The stomach, which for so long a period has been
at a stand still in its development, an to
grow its sides pushing out bet cor: the spigastric

::; cavities. The lumei
stomach and oesopli red ,Fi ;;.';- i.s .

landular structure which makes the walls or the
stomach co cor.plics.t~d in the s not begun
tc form in "H" the voile being simple and one cell
in thickness.

No figure of "H" as a whole object hoc been

reason that the skeletal plates should
be included end material adequate tc a complete study
of them is net in rr.y pesession.

RELATION OF LARVA TO ADULT.
THe hydroeoel is the first organ tc show radial
symmetry in the developing larva of Ophlura brevispina
and from the time when this organ has completed its

rotation about the oesophagus it shows a definite re-
lation to the plane of bilateral symmetry of the larva,

. The hydrocoeleis not only radially symmetrical
but bilaterally symmetrical, since it is divided into
symmetrical halves by the plane which passes through
radial canal 3 .and through the interradius or the
stone canal. This plan: coincides with the plane of
bilateral symmetry of the larva. She ether parts of
the star are built about fche water v r system

hence it as a whole bears a similar relation to the

•tl
larvs as was iniated by the hydrocoele.

No secondary twisting of the various part., of
the star occurs aeoi its relation to tL; larv» remains
constant s« It *-gan, and throughout t!*« life history
of the species the following statements hold truer-
ventral and lores 1 in the larvs are equivalent tc
oral and abcral in the adult. Although no physio=-
logical differentiation exists, if we regard that
part of the adult as anterior which wasantsriorly di-

N

rected in the larva^the trivium is anterior the bivium

is posterior.

*>

•->

In The foregoing I have- confirmed , in an ophiurid,
the conclusions drawn by GOTO from his studies on a
star-fish. In hie work on the development of Asterias
pallida GOTO(V) thought he was able to prove the coin-
cidence o5 bilateral symmetry, which obtains in the
adult star-fish, with the plane of bilateral symmetry

of the bipinnarian and brachiolarian larvae .
ofthe relation
The study of larva to sdult in the star-fishes

A

ie made most difficult however, by the independent

origin and subsequent twisting of the parte of the

' star. At the time of their origin no two parts of

the star bear the same relation to the larva. The

relation of each part to. the larva also changes as

■
metamorphosis proc:eds.

The facte just enumerated admit of ether conclu-
sions than those deduced by GOTO and no two investi-
gators have reached the same conclusion. IThe point
cf view from which the subject has been approached
is not the same in all cases but the results oitltned

by those who have studied the question frro einps.bl.e

QdtrmAk

ho vr eves? of being reduced to the same basis, that is:-

.anes^bilateral symmetry in larva

the relation of the pis

A

and.aadult . -

CUENOT (f.) in hie latest work denies the exist-
ence of any known relation between them.

•♦

SEMDN (il)^ working on a holothurian, found the two
planes in question tc coincide, but his conclusion
is based on the supposition that the dorsal mesentery
of the adult is the same- as that of the auricularia
larva, which supposition BURY has since shown to be
in correct

BURY (3); after working on members of all the
Croups of echinodermsj concluded that the plane of
bilateral symmetry of the larval form coincides. not
with the plane dividing the adult form into two sym-
metrical halves but?with the plan? of radial symmetry.

McBRIDES (£) observation on a star-fish, Asterina
gibbesa, led him to adopt about the same view as that
of BURY. He found that the plane of radial symmetry
of the star makes an angle of 70 °f ( but may, without .
error, be considered as 30*) with the frontal plane
of the larva. This is equivalent, to saying that the
. - - of radial symmetry of the star is parallel with
the sagittal or plane of bilateral symmtfcfcy of the
larva, and is also reducible to the statement that
the planes of bilateral symmetry of the larva and :
adult arc at right angles to ens another. Thus right
and left in the larva becomes aboral and oral in the
adult .

THe difference in results arrived at by GOTO

and McBRIDE are due almost wholly to the stages in the
metamorphosis selected in each case- for the study of
the question; GOTO selectin£ a very late stage when
the larva had all' but disappeared t while the stage
chosen by McBRIDE is an eerly one in which the rudi-
ments of the star are just appearing.

If the five groups of echinoderms have sprung
fromaa common stem after radial symmetry had been es-
tablished, then in $ho metamorphosis which is found
in all the groups , there should be discoverable a
unity of relation between larva and adult. It is
hard to conclave of the radial' symmetry of echine

dependently aquired by each grou-,
although it is easy to seehov secondary changes may
have arisen in the metamorphosis since the groups sep-
arate d .

The five groups of echinoderms stand isolated
one another almost as completely as does the
Echinoderm phylum from the other phyla of the animal
kingdom and it is not my intention at this time to
enter into a discussion of the interrelationships
of echinoderms. I wish however to point out an in-
teresting series of facts , illu jt/at ed by members of

«#

the- Asterid, Crinoid and Ophiurid groups, which nay
have a bearing upon the subject, and in the same con-
nection,! rich to call attention to how well McBRIDES
hypothetical ancestor or the Asterids and Crinoids,
( 9. Fig. . ) .when details are not too closely com-
pared ,fits into the facta of the larvs of O.brevi-
opina .

In one of the Asterids ,GOTO has shorn that
toward the end of metamorphosis the alnost complete
star sits as a cap at the posterior end of the larva
with its aboral end posterior , its oral surface an-
terior, the trivium ventral and the bivium dorsal.

In AntedonfliKe the star-f ish,the rotation '
brings the developing crinoid head to the posterior
end of the larva ;but differing diametrically from
the star-fish, in that the oral instead of the aboral
surface of the crinoid is posterior, but this diffor-
ence does not in any affect the homologies between
the two groups as has been supposed.

In Ophiurs brevispina th: relation of larva and
adult at the tir.« of metamorphosis is approximately
the earn: as ie shown in stage F,in which ventral in
the larva is ventral (oral) in the adult.

Now if we talis the ophiuran larva at star;: F
and imagine the disk to rotate in such a way as to

brine its oral surface- away from the larval organ or

vrliicfi

preoral lobe it fairly represents $hatA takes place-
in the metamorphosis of Antedon, but if we think of
it as rotating in the opposite way bringing the ab-
oral surface away fror. the preoral lobe* then it more
nearly illustrates the star-fish metamorphosis.

In Antedon ?as metamorphosis proceeds , the stem
is carried on to the aboral surface; while in the
star-fish the preoral lobe finally disappears on the
oral surface. In O.brevispina the place of disappear-
ance of the- larval organ more nearly recoils the
crinoid than any other echinoderm,the larval organ
being found in eorr.e of my oldest specimens as a
small knob near the edge of the aborsl surface be-
t-re on arms (I) and (V).

COMPARISON OF THE LARVA DF ANTEDON ROSACEA WITH
THAT OF OPHIURA BREVISPINA.

While I was studying the 1 irvae of Ophiura brev-
ispina, characters were constantly being found which
reminded me of the larvae of Antedon as described
by BURY (1). Some of these points of resemblance
ore no ioubt only su] ?rfieial but others are cue;.
as to make it worth while to devote a short chapter
to the pointing out of ths similarities of the two
larvae.

The entire ciliation of the very young larvae
gives place in both, to a series of transverse cil-
iated bends, five in Antedon ,four in Ophiura. Ths
band nearest the anterior end cf the Antedon larva,
however, is small and incomplete. Two bands only
in each case surround that part of the larvae from
which the iff; is form L.

Th: blastopore, in both larvae, after shifting
fro.1?. -for position to one on the ventral sur-
face, closes and the archenteron loses its connect-
ion v:ith the ectoderm oni lies free in the body cavit

In the seven day embryo of Antedon and stage

"C" or Ophiura the hydroooele is a horseshoe shaped
structure lying in the posterior ventral part of
the larvae with the open end directed anteriorly,
and in each coo; the piano or radial symmetry of the
hydroc I Ls at right angles to the plane of bilat-
eral symmetry of the larvae.

g In the formation of the paired tentacles from
the radial water canals the processis ce,~uri re-entrip-
eta33^y in both larvae, the second pair of tent* -
appearing between the first pair and the water ring,
instead of between ah: first pair an It. and ten-
tacle as is the case in the other groups of =chin-
oderms. -

In the five lay Antedon larva and those st
represented by "D" to "F" in Ophiura, the stalk and
larval organ are strikingly similar both in chap a
n ;ition, the tv:o structures being rly
directed in swimming.

The stem of the Antedon larva, as a result of
metamorphosis, cmoes tc be an aboral structure and
just before the disappearenee of the larval organ
from the Ophiura larva, it is to be foun;! a.s a small

Knob, not in the center of the abors.1 disk it is
true, but on its edge. In the star.-fishes it may bo
recalled that the preoral lobe disapp;-ar:; on the
oral surface of the metamorphosing star.

To the above larval characteristics may be
similaritiy which exists in the iicpccition of
fcfie alimentary and coelomic systems in the adult
form.

In both Crinoids and Ophiurids the digestive
apparatus is confined to th^ disk.

The body cavity is continued into and to the
ends of the arms. When a transverse section of a
pinule of Antedon is compared with b transverse
section of an ophiurid ar&, the following strifc
correspondence is found in the parts. Aborally, seg-
mentally arranged calcarious ossicles and muscles
are present. A continuation of the body coelom runs
between and oral to the muscles. Connected with
on each side of this central brachial body cavity
are two other cavities, the subtentacular canals,
These latter , in Ophiura, are connected with the
perihaemal space in each vertebral segment.

The radial water tube lies between the subt.n-

taeular eanals and in each segment sends out a pair

of tentacles.

Separating the radial water tujie from the nerve

1:: to be round the radial perihaemal sinus.

In Ophiurans a sub neural space- is present which

is not represented in the Crinoid arm. This is due

to the fact that in Antsdcn the nervous system is

superficial while in Ophiurs it has been invaginated

been
and with its invagination a space has also car^I .'

A

in below it.

LITERATURE CITED.

1. BURY. H. ••Early Stages in the Development of Antedon

rosacea."

Philosophical Transactions. 179*1808.

2. Bury, II. "Studies in the Embryology of the

Ecr.inoderas."
Q.J.MU.Sc. vcl.RO.

3. BUry,Hf'JThe Metamorphosis cf Echinoderms".

a.J.Mic.Sc. vol.30.

4. Cuenot,L. "Etudes Morphologiques sur les Echinodermes" .

Archiv.Biol. t, XI.

5. Goto, S. "The Metamorphosis of Asterias pallida

with special reference to the fata cf
the Body Cavities."

Journal cf the- College of Science. Imp.
Univ. Tokyo, Japan. Vol,X. Pt.III. 1003.

6. Grave ,C. "Notes on the Development of Ophiura

olivacea."

Zool.Anzeig. Ed .XXI I. No. 580. 1899.
> Krohrj

7. Lyman ,T."

8. Lyman ,T. " Report on the Ophiuroidea".

Vol.V. Challenger Report.
0. McBride,E.¥."The Development of Asterina gibbosa".

a..J.Mic.Sc. Vol.38.
10. Preyer,W."Ueber die Bewegungen der Seesterne."

Mitth. a.d.Zool.Stat. z.Neapel. Dec. 1886.
ll.Cay,T." Ophiura brevispina".

Journ. Phil .Acad. Vol.V. 1325. Page 140.
12. Ser.on,R." Development of Senapta digitata" .

Jenaisch .Zeitschr ,£ .NAturwiss .XXII .1388 .

EXPLANATION OF PLATES.

T] • figures ilustrating this ^jr^r were dr.
to the sane scale of magnification, 330 diameters,
and were reduced one half in reproduction.

Figures 1,2,4,6,7,0,17,31 and 32. were recon-
structed from series of transverse end sagittal
sections.

In ell cases the part Df the figure which is
1 • et the top oi1 the plate is either anterior or £&£.
ventral in the larva.

ABBREVIATIONS USED.

ael Left an*-? rocoele .

aer Right anterior enterocoele.

ap Apical plat ; .

an sin Axial sinus.

b Bl- stcpore .

chi ,2,3 ,4. Ciliat :d bonds .

eg Cireu] ves .

cm Circu! ■ nesentery.

op Cellul ;.r plug.

I Dorsal pore .

ee Epigastric enterocoele .

he Canal connecting Posterior

Enterocoele and Hydrocoele;
he Hypogastric anteroeoele :

hip, 1-2 ,2-3 ,3-4 ,4-5. -Inter radial pouches of the
Hypogastric enteoocoele:

hy Hydrocoele.

ips Inner perihaeinal sinus.

ipa::,5-i Intsrradia] pouch of Axial

sinus.
lo Larval organ.

n Mouth.

ni First pair tentade nerves.

nr Ne rve ring .

02 Oesophagus.

3 2_ Or 3.1 iislt .

o?:" Outer perihaemal rin^.

pc^ Par? canal .

p Po 3 1 e rior snt erocoele s .

pv '— Polian vesicles .

rad

n ^-Radial nerves.

rg ) Radial grooves.

rps Radial perihaemal, space

sin a Sinus "a".

sin "b" -Sinus "b" .

st S' Lai.

ss Subneural sinus .

s St omach .

ti First pair foot tentacles.

t2 Buccal tentacles.

wvr tf&ter yasc p ring.

1, 1 1, 1 1 1, IV ,V. Arm rudiments.

1,2,3,4,5. Radial water canals.

PLATE I .

Figure 1. Larva in stage "A" seen fpom the- right

side, the right half of the ectoderm. re-
moved and the mesenchyme omitted.

Figure 2. The same larva seen from the ventral side
as a transparent object.

Figure 3. Median longitudinal section of a larva
in stag:- "A".

Figure 4. A larva in stage- "B" viewed from the ven-
tral side as a transperent object.

Figure 5. Transverse section of a lapva in stage

"B" in a plane half way between the blas-
topore and the point where the hydrocoele
is connected with the archenteron.

Figure 0. Larva in stage "C" seen from the ventral
side ,the ventral half of the ectoderm,

the mesenchyme and part of the oesopha-
gus removed.

Figure 7. The left half of the same larva.

Figure- G. Transverse section through stage "C" in

a plane indicated on Fig. 6. by the letters
a-b.
Figure 9 .The reconstructed internal anatomy of a

larva in stag? "D" the ventral ectoderm
removed and with it part of the oesophagus .
Figure 10. An outline drawing of Fig. 0. on which

are indicated by lines the planes of the
sections which follow in Figs. 11,12,13
and 14.
figure 11 .Longitudinal section taken through a lar-
va in stage "D"in the plane indicated on
Fig. 10. by the line m-n.
Figuresl2,13 and 14, Transverse sections taken through
stage "D" in planes indicated on Fig. 10.
by the linos a-b,c-d and e-f .
PLATE II.
Figure 15 .Ventral view of a larva in staged" to

show the ciliated bands and first appear-
ence of the arm rudiments.

Figure 1G .Dorsal view of stage "E" showing the cil-
iated bands.
Figure 17 .A reconstruction of the anatomy of a larva
in stage "E'J the ventral ectoderm re-
moved.
Figure 13. An outline drawing of of Fig. 17. on which
are indicated by lines the planes of the
sections shown in Figs. 10, 20, and 21.
Figures 10,20 and 21 .Transverse sections talten through
larvae in stage "E" in planes indicated
on Fig 18. by the lines r-s,t-u and v-w.
Figure 32 Reconstruction of the anatomy cf a larva

in stage "G" .In this case as in all of the
other reconstructions the ventral surface
is up and the ventral ectoderm removed.
Figure 32, An outline drawing of the water vascular

system of a larva in stage "G"seen from the
ventral surface.
Figure 33. Transverse section of stage "H't

through the region of the stone canal.
Figure 34. Transverse section of a larva in stags"!!"
talten throng:, the stomach.

PLATE III.

Figure 22. Ventral view of the fully developed larva,
before metamorphosis has begun. Stage"E'J

Figure 23. Outline drawing of F-g.22. The lines in-
dicate the planes of the sections which
have been drawn to show the anatomy of
a larva in stage "F" .

Figures 24,25,26 and 27 .Longitudinal sections of
a larvae in stage "F" the planes or V
are indicated on Fig. 23 by the lines a-b,
c-d , m-n and x-y .

Figures 23,20 and 30.Transveree sections of a larva
in stage "F"the planes of which are indi-
cated on Fig. 23. by the lines c-o ,d-o
and e-o.

VITA.

The v.rritor or this paper was born to Thoms.s C.
and Anna, daughter or W.B .Hubbard ,on a farm
near Monrovia Indiana on January 24,1870.

He comp] t 1 the course or studies as given in
Common Schools of Indiana in 108G and entered

[onrovia High School the following year.

In the Fall of 1039 he entered Earlham Coi:
Richmond Indiana from whiGh institution, after com-
pleting the Science eou re 3, he was grs i 'ith
the degree of Bachelor of Science in 1305.

Between the times of entrance to and graduation
from College two year: were spent in teaching.

In the Fall of 1895 he entered the department
of Biology of the Johns Hopkins University making
Zoology hie major, and Botany ana. Physiology his
subordinate subjects of study.

lie has held a scholarship in this university

it present holds the Fellowship in Zoology.

The Summers of 97 and 'OS were spent in study
at the eea shore. The former in the Johns Hopkins
University Laboratory in Jamaica the latter at VTcods
Holl in the United StatesFieh Commission Laboratory.

May 1G, 1009.