Embryology of Turritopsis nutricula..

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THE
E;.;3RY0r,CGY OF STO:;OTCCA AFICATA
A-^:D
THE E'/'BRYGLCGY OF TUx^RITCFSIS ;:UTRICULA,

BY

sa:.'Uei. rittekhouse,

DISSERTATIOiN
SUBivilTTED TO THE BOARD 0? U: IVERSI7Y STUDIES OF THE

JCH:.S HCPXIFS UFIVRRSITY
IF CCFFCR..ITY 'AITH THE REQUIRE;,.EFTS FOR THE DEGREE CF

DCCTCR OF FHI'GSOPHY.

dALTI . ORE.
1905

n:i.(&hl

PART I,

;he

LiVERYCLCGY CF STOMCTCCA APICATA.

THE EMBRYCLOGY OF STO.'.iOTCCA APICATA.

INTRODUCTION.

The material for this research was secured, and the
observations on the living forn^s were made, during the sum-
mers of 1903 and It 04 while I was occupying a table at the
United States Fisheries Laboratory at Beaufort, i.orth Caro-
lina. Sto^otoca is not very abundant in the harbor at Beau-
fort, I found it, there as early as the -riddle of June. It
is niost Plentiful during July and early in August. A few
specimens may also be taken until early in September, The
eggs were obtained from medusae captured between July 10
and August 5. The adult a- imals rould not be secured in
large numbers; and, owing to the fact that each female lays
only a few eggs the material for embryological study was
limited. Therefore the greater part of the worlc the resuitc
of which are embodied in tis paper was done with living
material. All the drawings, with the excention of those
of sections were -ade from camera sketches of the living

2

forms, iilastulap and Dlanulae ranpjinR in aRe froT five to
twenty-seven hours v/ero prese.ved and sectioned for *.ho
study of the various stages in t.ho formation of the enXoderm
and the other features of develOT:ment which tna]:e thoir ap-
Dearanci dUx-infC this period,

I v.'ish to acknowledge my obligations to ohe Honorable
George M. Bov/ers, Commissioner of Fisheries for the privoleges
afiorded me at the Fisheries Laboratory; and also to thank
Dr. Caswell Grave, Director of the Laboratory for helo and
sug^:estions. The v.'ork -vas finished in .he Biological Lab-
oratory of the Johns Hopkins University. For the interest
shovm and for kind suggestions offered during my work I am
very grateful to Professor V;. K. Brooks.
DLHISCZLCS.

The eg 's are discharge^.! at about five o'clock in the
morning. The ectod^:r;:ial eDitholiun of the ovaries becomes
ruptured, in fac*. broken down; and by the movements due to
the muscular contractions of ihc nanubrium the egrs are sot
free into the cavity of the sub-u.nbrella. Then by the rhyth-
mic contractions of the bell they arc- forced out of the bell
cavity into the v/ater outside. V/hile the eg^s ai?o being

3

Icid the rnodusr. ron;ains at ono soot, unless disturbed .a-^d
Izeens \xv^ a continuous and rhyth:'io contraction and expan-
sion of the bell and oroboscis. Thuo as the- eprrs are liber-
ated, one, tv/o, or three at a time, they arc- alnost iri-iediate-
ly pass;:d out with the ..iection of ".he water from the bell
cavity. Thin process of dehiscence lasts for a few ninutes
durin.c^ which the iri^dusa remains at t-he bot^O" of .he aquar-
iun. All the nature eg£^s are discharged without inter-
niission in the process, unless the medusa is disturbed. In
that case it frecuently swins to another oart of the aquar-
ium and in a short tine comrences to discharge the egqs again,
The eggs i . the ovaries of Stomotoca anicata are usually
all der^osited at one time. Occasionally a fe;; inmaturo/ones
are left in ohc^ ovaries after i-he process of dehiscence,
y/hether these nature and are laid r.t a later tine, or -.vhether
they are reabsorbed I a:.: not able zo decide.

As stated above, the egjTS are laid at about five A. iJ.
On several occasions I observed the ■ rocess of dehiscence and
found that the tine was always Dractically the sane, Sone
nedusae wore watched all night, July 14. At five o'clock
in the norning they began to lay their eggs. They all began

4

at about the same ti-ne and all the e^c^s were discharged v/ithin
fifteen or twenty minutes. The time when the -nedusae are can-
tured and Dut i!ito aaua^iuTi does not seen to have any.i--
fluence or, the oeriod of dehiscence, I have taken them in
the tov.' at nearly all hours of day and nif^ht, and never had
them to denosit their egejs excecL at 5 o'clock in the rooming,

THE SGG.

The egg of Storotoca ar>icata is soherical and noasures
« 14 of a millir.eter in dia-etcr. It is devoid of a -rerbrane
and the cytoolasn is rather dense and only sc-r.i-transoarent;
however iL is not ac ;ense as the egc: of Stornotoca rugosa,
which is extreniely o: aaue and of a challcy-whiLe color, and
also slightly larger. The color of the eg-^ of Stpinotpca
apicata is a bluish--./niLe.

A point of interest may be mentioned in this connection.
On one occasion, having taken a nu-'ber of Sto^pLoca in the
tow at night, they w. re picked out and out into a dish of
clean sea-wate:- with ohe intention of allowing them to lay^
and using the eg.'^s for study the next morning. It han :ened
that both S'-ecies of Stornotoca that are found at Beaufort

5
were ronresented. There v/ere mature females of both soecies
that deDOsited their eg'-2 thr next morninr at tie re.eular
Deriod; Stofr.gtoca rugcsa has the same time for dehiscence
as StgmpLOca apicata. Only tho egps of ihe latttr sDecies
develo ed; there being; no jialea of Stpr-otoca ruggsa. The
next day when the lwo soecies wer.^ in Ihe sa;ne dish, and both
discharged their egps , only the eggs of Stgrr-otoca rijgosa.
segmented and develced. In this case there were no mature
males of Stpmptpca apicata. These facts aroused my interest
and on several later occasions I ola^a the two species to-
gether with the intention of vetoing them to interbreed,
but did not succeed and therefore I am led to the conclusion
that, they will :;ct cross even though they are soecies of the
same genus. To my icnowledge no other exDoriments have been
made in attemoting to cross different s.:ecies of this group
of animals, and I did not have the onrcr. unity to try v/ith
any other s^'ccies than the above named after my attention
had been called to the fact that they did not/cross when ac-
cidentaly placed in a dish together,

POLAR BODIES.

Soon after the egg is denosited tl.e first pclor body

6

is f;ivon off. A few iniiiutes later the second Dolar body is
forrnt^d. They remain near the egg for some tiihO; frequently
until after the second or third segirientatior; . The oolar
bodies are not held by a merribrane, as the egp is devoid of
such a structure; neither are there any pi'Otorlasmic con-
nections visible vath a inagnif ication of 212 diarreters. Yet
for a tine they seem to be held near the egg by so^e r.eans
of attr^tction. The first oolar body -ay segment once or
twice. Usually about the time of the second cleavage the
polar bodies eiiher disintegrate or pass out into the water
and are lost.

JSRTILIZATIOl^i.

Very little concerning fertilization could be -.Tiade out
on account of the character of the eg?. The ova and spcrn^aia-
zoa are discharged irto the water and there fertilization
takes Place. It is i-::ossible to folio., the nuclear changes
which take olace during iiaturation; or the union of the rr;ale
and fen,ale proruclei in the living ege because oi the Jensity
of the cytorlas.T, and material could not be secured in suf-

' A

ficient abundance in the various phases for the preservation

7

of the different stages for sections. There is no visible
fertilization-ir.eiTibrane Riven off after i-he Denetration of the
snermatozoa.

CLEAVAGE.

Cleavage is total, equal and nearly regular, esnecial-
ly in the early stages. The divisions occu:- at short inter-
vals, and the blastorr.eres soon move away fro:r; the center
of -he egg, thus foriTii-^g a gradually enlarging segmentation
cavity. The cells continue to divide and arrange themselves
into a single layer around the blastocoele to forin a true

no

tative oole as the deutor laclm and Dfotoolasp are distributed
evenly in all carts. But as is custcxary and for convenience
of descriDtion I v/ill call the oart of the ovum froin which
the GOlar bodies are given off the unoer oote, and the Dart
of ohc egg OD osite che lov;er Dole,

The first cleavage occurs a short tirr.e after the oolar
bodies are e.iected. The Diane of division is vertical; the
segmentation-furro'iv begins at the upoer pole and gradually
deepens ur.til the egg is cut into two equal parts. The egg.

8

vipvfed frcni above, at first shows a nenrly circular de-
nression v/hich vpry soon sTDreads laterally and begins to
grow down. This first furrow is wide and leaves the blasto-
n^eres se^^arated s^-^e distance frcr each other as it rrc-
gresses downward, as is seen by loo'/ing at the egg frop
the side (Figs. 4 and 5). This furrov retrains oren u-^til
the egg^is alnost senara'feed into tv,-o narts: the blastoTeres
being connected sirrnly by a narro-^ orotoolas'nic fil- at
the lower "Dole. Prctonlas^iic currents can freauently be
seen in this connecting thread. Bu'^ting ('93) describes
and figures in Hydractinia a Drctoolas-ic thread in the two
cell stage in whi^h she also notes ^rctonlas'-i'^ roveTents.
The con-^ecting fil'^ in StOTOtpca anicata is not as clear
and definite in outline as she shows it in her figure of
Hydractinia. The two cells gradually -O'^e in close nrox-
i-ity and in a short time the con-ection of orotonlas'n at
the lower oole is broken and the ccrnlete two-celled stage
is forn-ed (Fig. 6).

9

The second -^lanr of divisior^ id also n^oridional and
at riPht anp:ler; to the first. This '^leavafjr takfis nlaco
about fifteen -inuter- after the first divisio-. Those
secor^d soFT-entation furrows start ^t the centre ?.no -ove
out toward/the periphery. Durin,? their progress outward
there are to be seen globular or oval snaces at their cuter
extrcTities. These spaces are large enough to cause open-
ings that exterd through the egg as shov/n in Firure 7.
During this cleavage there is a shifti-g or rctatio- of the
blastor-errs fro^ right to left. The second seg-^entaior. fur-
rcr.'s usually start op'-osite each other at a point in the
centre of the first cleevage furrow, and then arc carried
apart by the rotatio":. Or the rotation Ty heve started
before the second segTentatior began; in that case the second
cleavage '•lares are soT.e distance apart -s soon as they
make their appearance. Figure 7 shov.'s on egr in the '^re-
cess of divisir^ in which rotation has taken Place, During
the progress of the second seg-entation , the ep.f^ hns fre-

10

oup'^tlv a flattened p.nr^parnce as Boen i^i tho fif^urr iust men-
ticned.

In this staR'^ -nroto^las-^ic filps or bridge?, also,
frequertly exist for a tirr^e after the seg^entatior is practi-
cally complete. They finally are absorbed by the blasto-

ce
'Teres v/hich rcmd ur> for-ing the co-rleted four-j^lled "tage

A

as shown i-i Figure 8.

The third cleavage r>lane is equatorial and divides the
egg irto eight ecual blastOTeres ; four of which are situated
at the ufner riole and four at the Icvrer role of the e^!? as
seen in Figure P. This is the condition when the c^nditixsp-
is regular, and rnirht be described r.c two four-celled stages
of half size sunerir^osed one unor the other, an'^ ' then the
uooer set rotated to the left. V/hile the fcr^^aticn of the
eight-celled stage was always nearly the sa^-e in the eggs
that I followed, after the divisio-^ was comnleted, the
blasto^eres did not always retain the s-'ttc relative posit-
ions Sometires there occured a senaration of the cells at
one sidr of the eouatorial furrow and the blastcreres rolled

11

apart jr zuch a -r.rner an to forin a curvec sheet. In others
this separaticr ard virrcllirp: of the hlastomeres was lers
defiritehr'd the final arrangement v/ac such as shorn ir Fip-
ure IC.

The irreriilarity ir the relative "ositior of the blasto-
rereslberins rith the eight cel'rd stare ard is r-rre or less
charaeteristic of all later stages ur to the f creation of
the blastula. But, while there is diversity of arrargerent
of the bi astc-eres , reverthrless I ar led tc believe
that the civisior of the individual cells is regular and
takes .iust ar though the blastcreres alv;ays held the same

A

relative nosition.

The fourth. segTentation foHcvs after a short ner^od
of tine. Figure li Ehov;s a sixteen-celled stage v-hich is
nearly regulrr, but the cleavage cavity has already been form-
ed v,'lthin the rassjof blastcreres a-d they are thus nushed
av/ay fror the centre of the epp. In this stage the cell
lineage can still be traced even i^ the forrrs that are scre-
v-hat irregular. But in -.hejblder stages the arrange-^ent of

12

the cpllc- is iTore irropulrr r.rd ovhtif: to the- cracity of the
egg it is difficult to follov; with accuracy the derccrt of
the cells. Frgure IT. rhcv/c a ]atcr stare in v.'hich the ar-
ranperert of the cells is mere regular than is frecuently
TTiet with ir eggs of the sane age.

As strtod before, the divisiors follov/ each other at
short intervals. \Vith:n tv;o hours after the eggs vrere laid
they had undergone the ^rocess of laturatior a-d fer-
tilization, a-d had "passed beyc^d the sixty-four celled
stage, ;he cells continue to divide with the sa-e raridity,
while within the^ ihe cleavage cavity is alsr gradually en-
larging. Finare 1." shows a stage in v.'hich the cells are
more or less definitely nlaced around the segmentrtion cavity.
The blastoreres fi^^aHy beccT^e very numerous ard srali,
ard arrange the-selves around the blastoccele in a single
celled layer for'^ing a true blastula.

BI.ASTULA.

'he blastula ir oval in share, and is but slightly

13
Ir.rpor thar the ursepFPrtcci err. The avfra^e r.i2c c.r several
blactulpe that were reacurec' war .19 nr. ii" lenpth a-^d .15
mr. ir their larre?t transverse diareter. The epr before
cleavage '-easured , as stated before, ,14 tt. ir di^areter.
The blastoreres i'^ the blastula r^tape have berr-e very
-unerous a^d ?~all, ard are arrarf^ed ir a zi^.f.'e layer of
epithelial cells, V.hen the larva ir. about eif^ht or ten
hcur2 eld, these "oerirheral cell? '■''evelOT- cilia; nrcbably
each cell has one ciliuir. Vith the develorrert of the cilia
roverert cctr-e'-ces . At first the nrtic is sllrbt; b',:t
as the cilia beccre -"-ore ru-erous, the blartula is er?-bled

by the ciliary rrvererts tc leave the bctto- rf the aauariur

-to-
urer rhich it vas heretofore lyirp a-d^svir a'-cut 1- the

v.-ater with s sriral cr ccrk-r^crew motior v^Mch is charac-
teristic of hydrod blastulae ard rlrrulre. Ihe larpe erd
of thp blastula is r'irtcted forwrrd a-d therefore rray be
called the a'terior e-d. 'hether .hr rnterior rart of the
larva ccrresrcnds c the ur er or Icv/er role of the egg was

14

ir'-ossible tr drternine. It ir rear.onable , hov/ever, tc infpr
that thPTP iray be no fixed rolarity ir the- Irrva of Hydrr-
rredusae, for it is v.-ell Irnown that ncrral prbrycs of sr^all
sizp vrill dpvel cpe frcr, fra^repts of eggs.

FLAyULA.

The blastula Frar'ually elonpatf?, ard beccires narrovrer
fer'-irp ? larvr which if urually about three tirer as long
as bread ard krowr as a rlarula. 'Fvor, reasurererts tal-en
of livinp; rla'-ailae the average rize is about .25 mm. in
length a-id .OC tttt, ir the short dia-etrr. These rearure-
rer-ts are not constant, the larva beccTi'^ig sojev/hat longer
at an older age. The anterior end rerains slightly larger
than -he rosterior, but the difference is net as great ar
in the blastula. During the bias tula stage the larva sra:
near the bottor of the dish; v/hen it attains the rOarula
stage it rises a-d svdrs st er near the surface ef the
vater for a shorter or Icnger tire. Ihis phenorrenon occurs
about tverty-fcur hours after the ergs are fertilized.

15

Aftrr spvotri hcurs the rlnrula pradunlly npttlpr, toward
the bettor apain ard f orally the ?r"ira3 rover entr ceare,
due tc the loss cf the oilia. lor a time of vr.ryi-p; lo-pth
after the P-iral -otior stors thr rlanula glider alorr or
the botton of the araariur. About forty-e:ipht hours after
the egjTS are laid the larva reaches the stage of develo--
ir.ert ir v;hirh attrchrerit takes -lace. In rre-aratior for at-
tachrrrt the plarula rettles to the bettor, loses its cilia
ard ceases ite- rovererts.

FCE!/ATIOr OF THE ECTODE?.;'.

The forratio- of the ectoderr in Stcrrctcca a^icata is
siir-le ir ccr^rariso^ rith these species i'- v.'hich the segrer-
tatior of the egp is ur.eoual, rivirp rise to racroreres
ard ricrcmeres; ard i'^ which the ectoder^ is forr^ed by a
ra^id i'-'crease of the nicroreres a:xl overgrov;irr of the nacrc-
ireres by the rrrcess rf eribole. Ir Stoirotrca or the ether
hard the oleavare is equal and at the ccrrt^leticr. cf seg-
i^ertaticr the blastOT-eres have divided irtr cells of uri-

16

fcrr size ard are situated i^ a rinf^le erithelirl Ir.yer
r.rour.d the :-eriT:'hery of thr blartula (fi.rures 16 and IV
shcv; ?.pctic?s of blastulae five and eipht ard ere half
hours eld resreetively) , Thur , frc:- their resitirr, all
the cells v.'hich result fron the sep^entatic of the epp di-
rectly ray rrcrerly be refjarded as ferrying ectoderm; and
indeed "alreac y at this stage cf develonrent be desirnated
as such, v-ere it -rc-er to use the ter:- ectoderm before
the ar-nearance cf an inner gerr layer. The cells of the
blastosrhere are cclurnar in share a-'C at first all are cor-
T^aratively of the srre height; but finally those cells rt
the nosterirr e:-d become screv;hat taller than the rer-t.
This is the region v/here the endcder^i- vail be budded off.

for;.: AT I ci: of the ekdcder;-.

In Stomctoca the fopT^atio' of the endoderr tal:es nlace
by unipolar ingression, or ":he "hynctrone" method. The
latter ter~ was use: by i-.:etschnil:off in contradistinctien

17

tc ir.ultiDnlar mif^rcitirT^. l>^ the rultirc\ir fcrratior of
the rr^doderr he distinruiEhec four different nodes, nare-
ly: 1. A rri-ary delarrinatior v,-hich takes rlace by a trars-
verse diviricr of the blasted err cells, and occurs ir the
Geryoridae ard Eudepdriuir . ?., A irultv-clar inpression
;vhich takes ci all sides ( Aepinc-sis) . 3. /. secondary de-
la-inatio" -vhich occurs v/here a rrrula structure exists, as in
;^£lliyra, i'hcralcrera ard in irort of the hydro id rolyns.
4. A irixed delairiraticr i' vhich the endodernal cells orig^ir-
ate ir rart throuph transverse divisicr or i'^Fressior; ard,
also, thrcuFh subsecuent differer tlaticr as a secondary
dela-iration. This last rode of the fcrTratio- of the eelc-
drr-r, accordinp to : etschrlkoff , occurs in Fplyxenia; and
is the transitional ^^ethod between Triultinolar nitration
a:^d enibole. In the urirclar ingression, cr "hynctrone" nrc-
ccss the for~atio" of the endoderr is confined tc a rc-
naratively snail arer at the nrstrrior end of -he blastula.
This is the irethod that is follov-od ir the species under

18

ccrsidrrrtior.

About the tirrr the blactula becore?. ciliated ard be-
gins to sv;ir, usually eight to ten hourn after f ertilir:atior. ,
the cellr. at the ^'octerior end of the larva becore so-e-
what tal'er thar^ those i-^ the other regions; and fro'T^
these cells relatively few in nunber, the endoderr^ arises.
The for'-atior of the endoderr in Stprot'oca is, in a general
way, siriilar to that dereribed by letschrilcff in his
"E- bryolcgische Studien an t-'edusen " for Clytia f l^'Vicl"!^.,
Clytia virid leans and Cctorchis Gepexbauri . The endoder-
nal cellr are river^ off frcF he Icv-er end of the blastula
and are Dushed into the blastoccele. At first a single cell
ray be budce^' off. Gradually more cells are given off,
and those first set free divide; sr that byjthf crntinuation
of this nrocers for an indefinite ti^^e, the blastoccele be-
ccTes filled solidly fror the a-terior to the nostericr
end. Pictures If, 1£ and 20 are frcrr sections of blastulae
in Vi'hich thr fcrration of the endoderr ir ir different

19

stapen of rropress; a-d ir Figure 21 the endoderi?al tisnue
has filled 'he entire cavity.

/.ccordinp to ; etschnilrrff , i- his descrirticr of uni-
rclar injures si en or "hyrctro-e, " the erdoder^-al tissue
arise? as a rule by bodily ■■iFroticn of endoderral cellr irtn
the blastocreie, and net by a transverse division of the
ectodermal cells — the inner rarts pcinp to fcr^ erdoderr
and the outer narts re-aininp as ectoderral cells. In
Figure 2C, Plate 2 ;.'etschnil:off shows a cell in -,he nrc-
cess of tra-^sverso division"; ar^r in Finure 21 of ihe sa^e
Plate tv/c cell;? are so situate(" that one can easily i-^fer
that they riay have a'.'^isen hy transverse division of a sinple
ectoderT-a" cell, Thene flpurer- are of Clytia a'-d i'^ his
descrintir" of the saTe sr.ecies he rro'-tli^ns the '^ell in Fig-
ure 20 as the O'^ly one that he r'ound in which transverse
division- occured. This he seers to regard as an exception ,
and claims that as a rule the ectoder'^al cells increas- by
longitudinal division and rrigrate i^-to the interior.

?.'y Traterirrf for the foi^rrtior of the endodprr in

A

Storotoca vas scarce and it in rot inrcssi ble to have -ris-
intrrrrpto'^ tho ':'ho?^0'^ona, Hov.'ovcr,! a"^ ir^clined to thinl:
that the c^doder-a" cells arise by a trarsverse divisior of
the ectodernal cells, as Vetschril-'off sho'vs ir the ex'^ert-
ioral case of Clytia viridlcr^s. Fipure IB is drav.T frcr
the c-l}' secticr I ^-as able to seciire frc rreserved "cterial
showing the bp,?ir,rirp; of the for-rtior of the e-doderr, and
that^ras cut rlirhtly ^blioue, causirr ?.C'-e doubt. A
sectior of a little older stap-e a^d drawn rith hipher r^agni-
ficatio" is shOT/n i" Fipure 19. Here there are three cells
that an-e-r to have lust divided by trarsversr division,
/.nother reason which causes ire to thinl: that the e^^doder'-al
cells arise by transverse divisic^ of the criminal ecto-
derF cells is "he fact that thr ectcrerrrl cells in this
repicn are practical ly as ride as those i^^ other rarts of
The blastula. This v^uld liot be the case if the lonri-
tudiral division cccured: for necessrrily cell division

21

is rorf ranic ir the rr.pior v.-here the pr^dndorir is river
off, ard ccnsecuently the cells v.Tuld be ^arrovjor. U^-
fortnrr.tely , because of scarcltj^ cT raterial, the exact
cellulrr details cf the for-atio- of the e-doderr v;ill
have tr be left for future study.

The ripration of the erco'er'' ccrtirues frr scFe
hcurf^ , ard firally the blastccrel(\brcr'-es sclidl^'- filled
v;ith this nev/ly developed tissue. At first the cells are
crowded tof^ether, frecue'^tlv q-dte dersely, without any
definite arrarpe-^er.t except that due to rressure. Ther

those cells that are situate'" next to the e'^tc-ler'^al layer

e

cha-fTc i* sha'^e, beco"-«=wF colu-nnr a-d assu^^e the a^'-earance

of a "ore or less cistinot layer. Such an arranf^ene-^t is
shov/n i-- Figure 22. Later a seriaration talces rlace in
the centre of the en^derrral -ass. This is the first be-
pin-'inr cf the coelenteric cavity, v'hjch Pra-Uially in-
creases in si:?e; and finally the c-dcderral cells oecoTe
arranped in a sinrle layer around this cavity.

22

DIFFEREMTIATIC;- OF THE ECTCDERMAL CELLS.

I'her the Irrvr. is ab'^iit tv/enty-f^our hourr old r.rd
about the sr.'^e tl-e that the PTiclrderrnl tissue hoFins tr
arrar.rp itself into the definite irir'er rerir layer, a d:f-
fere'^tiaticr corr^PTice?, ir the ectcderral tissue. The inter-
stitial ce]ls row ra!-e their arrearance here a-d there by
crcv'dirp ir betveer the base? of the ectcderral ce!ls.
These latter cells v;hich heretofore r/ere straij^ht cylin-
drical structures v;ith their sides parallel to each other,
now becc^e ^-cre irre.pular; sone aspu'^e '^cnical f crTrs , others

CO

s'^i^dle shaiies avordinp to the rressure of the neiphbor-
inp cel?.s. Also, about this ti-e, or a little later, STiall
oval refractive ^odles ''al'e their a'^-^eara-ce urually ir
the i'^terstitial cells, occasio-ally i?" the ectoderra" cells
also. These srall cvcid structures rrarually ^-ush their
ccy tov;ard the exterior, ard finally cop to be situated
i-. or betv.-eer the ectoderr?! cells rt the surface. They
are develored irt^ -pratocysts .

ATTACH' FI T.
Vhrr thp larvr is rbout forty-eipht to fifty hours
eld it sPttlPE tc the bettor, loses its cili?. ?r>d thus its
ncveTer:ts eesse. It is vor rerdy to hercr-e cttacher' .
Tho -ethod of r.ttrohrert ir. Sto-otcoa differs fro- th?t usu-
ally described r.-d rhi.:!. -1"- rrrarded as tyrlcal for the
hydrold larvr; in v,-hich ease they settle dowri on the bread
a'-tericr e-d, frcr rhieh the hydrorhiza are piver off,
v.'hile the c^rosite end forrs the hydrarth a-d develors
the -outh and tentacles. The rlrrula of Sto^otppa instead
of settlinr down o^ the anterior end, beceres attached by
the vhole le^^.rth of the larva. That ir, the rlanula does
net becoTe trarsfrrred into a hydrarth but fcr'-s the root;
arc the first hydrrrth is piven off frcr. the root ar a bud.
The nla-ula chnnpes its sha^e about the ti-e it is readi f or
attachrfrt. The e'larfred anterior end is reduced in sir.e
a-^d the ^ arva becer-pc snindle shaned. Then usually about
the tir-p tho bud vhich will forr the hydra'^th annears, the

24

'^rirar;^ rc't bra-^r^hes, rivinrr c,ff: one or '.'.vc seccr^dary
roots; so that v.-hen the hydra-^th is develcrpd it rfiay have
tvc, thrpp or four hydrcrhiza, e? shew-" in Firurer. 27 - Z2,
The settlirp- drvr a-d attach-iert of the ^lanula of Storno-
toca aricata is vnry much liVr- that ivhich takes -^.lace in
Turrito-'sis nutricv.la, the develo-rrTit of v/hich v.'ill be
described ir a- other rearer.

Frcfe::scr Brccls ir his v/crl" or "The Life-History of
Eutira" (I'c^) has shcwr that the rlarulae of Eutira,
Tuilii-Prsis and Hj/dractiria fcrr rccts a-d that the hydranths
arise as buds fror the roots.

DEVFI.'-^-rFJ'T CF THE HYDFA'TH.

Zfter the larva han becore attached it very s'on ce-
velc'S a bud, f^ererally at about the ce-tre of the root,
v/hich is the bepin-inr of the hydrarth. A circle of srall
prelections irake their anwearance very enrlv around the dis-
tal end of the hycranth bud; ther^e are the rudinents of
the trntacles a-d are usually fivr i- r-u'^'ber. Cicasio'-ally

25

a hydranth bud is -et with v.'hich has six tnntncular rrr-
.-iecticps ard thus rives rise to six rri'-'ary trntrrles.
The -^outh is '^ov,' devplcred, as r. slit breaking thrcurh the
two ger-^ layers, at the a-pex of the yourr hydra-th i-^ the
centre of the '.vhorl of tertacular buds. About a day later
T-ore tentacles a^^r^ear. These secondary tentacles alter-
nate v/ith the '-'ri-ary ones. The secondary tentccular buds
do not all arsnear si-^ultaneously; but are usually added one
or tv.'C at a tire u"'til the second cycle of tentacles is rorr--
rleted and the hydra-th has ten te-tacles in all. :hus
we ray have ycu-^F hycranths vnth six, seven, elrht, n:ne or
te- tentacles acccrdinp to the stape cf revelcrrent.
Ten seerrs to be the nuTber cf tentacles in the fully
develc^ed hydi;!/^ rclyn. The oldest nolyps thst I reared
five days old ha;' this number; and Professor Brcol's described
the hydr,3/0d, yhich he found or the Icrer surface of the
shell of the livinr li'ulus, arid which had -edusr buds,
develcned, as hcving only ten tentrcles. The hydra-^ths

26
thnt I re.Ted i- the laborr.tory rorrer.r)ond ^^ith those found
by Professor Brc^l-s a-d I he.ve pc doubt that they are the
sp."-e s'^ecies. The '^rirrary and jccoMdary tentacles arise
frc" the ca-e level so that they rray be said to ecrstitute
one -hcrl. The five rrlrary tentacles, ho'.vever, are lenper
and Drc.iect forward; v/hile the secondary ot-cs a.^e shorter
a-d extend backvard. The tentacles are veil ar-ed with thread
cells v.'hich are arranged around the tentacles in clusters
at short distances frcr each other, frc" one end of the ten-
tacle to r.he other. These f^rouns of thread cells\becore
closer topether as the distal end of the tentacle is an-
nrcached.

A thin delicate ^erisarc is secrete^ early i?' the devel-
crTrent of the hycra'-th. It adheres closelv t^ the root and
ster. It deer not extend the e^^tire lenpth of the ster;
but stons a little distance below the 'ircle of tentacles.
In Flpure 31 a nrlyn is ^r\\- i" v.-hich the ccencsarc has re-
tracted for some distance in one of the hydrorhlra and

$?7

left, the delicpte tubo of r^erinarc PT'ity.

SUMIv^ARY.

1. Tho effps are Inid at a rfir:ular ti-e, about fivp
o'clrck ir the rorni'p. They are set free by the brealrinp
down of the cithelial layer of the ovaries.

2. The pgff is s-^herical ard -easures .14 Tn". in diaineter.
It is destitute of a -e'^brane v;hen laid, ard nore is subse-
cuertly develrred. The oytorlasr is dense a•^d oraoue,

3. iVaturation takes T)lace after the epps are laid; ard
fertil izatior takes nlace very soon. Eetails of fertilization
could not be Tade out because of opacity of pg?s .

4. Cleavage is total, ecual ard '^early repular, es-r^ecial-
ly ir the e?rly stapes. Frctclasric threads or bridges , ccr-
'-ectirp the differert blastoneres durir.p the early cleavapes,
are frecuently encountered. The sepTe^tinp cells arranpe
themselves arcurd a coi^tirually enlarpinp cleavape cavity.

B. At the co^rletio' of the sep-^entatior a true blastula
is forred, v/hich develcrs cilia a-d sv/irs with a spiral
rotion. 'Ihe oval blastula elrnpates and is transferred into
mlanula.

6. Thr ectocerr r.rirrn dirrrtiy frcr- tho npr^f'Ptr.tior
cells v'hirh r.re prrr.rped ir r. rrrirherrl layer arcurd the
Mast"ccrl p.

?. Jhe frrraticT cf the e^-rccerr- is by u'i^clar i^-
rressior. The Cfllr. at the r-csterior end of the blar,tula
hud off the T:ri:^it-'VP rT^doder"- ti^isur v.'hioh riprater. into
the blastoooele; a^d later is arranged irto the inrer perir:
layer.

f. ler-atccysts arise chiefly in thf Interstitial rells,
soretires in the erdoderr, and riprate to the surface.

G. The larva beccies attached by its side and is trans-
for-^ed irtc the hydr'^rh^za. The root frecuently branches
s^cr after attaohnent.

10. The hydrar.th develor.s frcT a bud, v;hich is piv^n off
frcr about the centre of the hydrorhisa.

11. The tentacles arnear (^arly r." ---^i' -:-^ ^^^■^_ir'^,s at
the distal '^art of the hydranth bud.

12. A thin delicate nerisarc is :^ecreted '^r-'^-r-'^ the
hydrcrhiza a-^d ste'^ un to near the tentacles.

29

FART II.

THE

EMBRYCLOGY OF TUREITOPSIS KUTRICULA,

30

THE EMBRYOLOGY 0? TUPRITOPSIS I'UTRICULA,

INTRODUCTION.

This v/orl: on the enbryolopy of Turrjito^sin nutricnla
',vas bPguT! at the suggestior of Profonr.or Brooks. The rate-
rial vms collected and the observations on the livinp; s-^eci-
mens v/ere made durinfT the surTi-^ers of 1903 and 1904, v/hlle
I occ'.iT)ied a table at the United States Fisheries Laboratory
at Beaufort, h'orth Carolina, TurritoT>sis is one of the -^ost
common TDedusse in the harbor during the sunder. In the two
years that I v/as there they became abundant in the begin-
ni'-g of JuJ-y and rsTained -or? or less Plentiful until I
left Beaufort Se-!^tenber 13. "Ahile the medusao could be col-
lected in fairly large nu'^bers, many of them were irr-aturey
"^hey lay only a lini.ted ^umber of eg.crs. However the 'material
wan r)reserved and sectioned for the study of such facts as
could not be made out froT the living fcrrs. The w^rk v/as
finished in the Biological Laboratory of the Johns Hopkins

31

Univprsity,

DEVEL0PME:;T of the CVAPJAri EGG.

The ova develo- in the ectodermal layer of the Tianu-
brdum. The erithelium becoites very ruoh thickened i^ four
regions; these enlarf^ed areas for- the ovaries. The oriin-
itive ovarian cells when first differentiated are larger
than the ectoderiral cells of other -oarts. Their nrotcplasm
beccn-.es hoirogeneous and of a finely granular character.
The nuclei are less hyaline in aDnearaiice j and the nucleo-
lus stains deenly. The -ri-itive ova are first distinguish-
ed fro": the rest of the ovarian cells by the increase in the
density of the cytoplasm and the enlarging of the nucleus.
The latter becoiies very large in nronortion to the size of the
cell; and acquire.: a vescicular character. The nucleolus is
cons"icuous, and a network of chromatin is scattered through
the ger-inal vesicle.

The nri'itive ova gro^.v by the absorntior of the ovarian
cells around the-. As gro;vth takes nlace there is a change

32

in the characterpf the cy^orlasT, It loses its horrogene-

er
ous and finely f^ranular nature and develo::3 a suT^nly of deut^o-

clasTn in the fort of yolk granules. These are large and stain

very darkly. They first aorear around the gerrinal vesicle.

As they be3o;r:e more nuinerous by the continual formation of

new ones, they are oushed out through the cytC'lasr toward

the ^.eri-hery. The formation of the yolk ST)heres goes on until

the ovum is densely crowded v/ith thea exceot for a narrow

Derioherl zone, in v/hich the proto'^las" retains its honno-

geneous and finely granular character and forTS the ectonlasn^

of the -rature egg. Figures 1 tc 6 inclusive show different

stages in the develCTent of the ovarian egg and the forn^ation

and 'Tiigration of the yolk granules. Soine idea of the extent

to which the ijrotoolas'n becoTies crowded with s'oheres of

deutonlas" can be forned fron Figure 3, which is drawn fron

a nearly nature ovum. In the fully develoned egg the layfr

of ectonlasT is narrower than is ronresented in this figure.

The yolk granules first arj:";ear around the nucleus of the

33

ovum; and it is not in')robabl*^ that they are, in nart at
least, the result of nuclear activity. During the formation
of these bodies, the nucleolus shows signs of being in an
active condition and ^ay also be connected with their manu-

A

facture. In sorr.e stages the -'urleolus is der.se a-d horno-
geneous; in others iz has one or tv;o clearer globules in
its interior. These facts see-i to show that it is not in a
dormant state; and it is DXossibe that it -ay be associated
in some way with the transformation of the absorbe ; nroto-
nlasT into deut^cnlas"^ At least that the yoll: spheres arise
directly through the activity of the cytonlasr;, indepen-
dently of any nuclear or nucleolar function, is doubtful.
£er If aa^ were the case we wou.ld exnect the yolk bodies to
arise in other parts of the cvu~ than around the germinal
vesicle. Thai this orcurs there is no evidence from the studj
of rrany eggs, The primitive ovarian cells are all, or nearly
all, absorbed and used in the ranufacturo of the yolk gran-
ules by the growing ova, except a layer at the outside v;hich
is transforTed into the emithelium of the ovary. The cells

34

of the ovariar v.-all are s::iall and soinev/hat flattened. Their
nuclei are about the same size as the nuclei of the nriiitive
ger- cells, but are less dense. The nucleoli rre con-
spicuous and stain d.eply. In genera' the cells of the er)i-
thflium of the ovary are sin^ilar, excent they are not as
much flattened,) to the cells in other narts of they^ctoderral
layer of the subu^brella. The eggs in the ovary lie next
to the rr.esogloea, that is, there is no ectoder-.ai tissue
betv;een theT and the supr)orting layer. The ovarian eggs are
irregular in shar^e due to their being crowded together; but
v;hen liberated£hey becoire spherical.

DEHISCEi\CE.

The eggs are imbedded in the ectoderr-al layer of the
manubriuT:, As the ova grov; and increase ir size the epithel-
iuiT' of the ovary becomes -ore and more distended, when they
have reached aturity the outer ectodermal tissue of the ovary
is under r-onsiderable tension. Finally v/hen the time for de-
hiscence arrives, the outer wall of the ovary is runtured
by the aid of the ruscular contractions of the manubrium

35

and bell and the ej^gs eccare into the acvity of the- urbrella.

The rrocess of epp laying is very nimilar to that described

for Sto^^.otpca.

The number of egfs denosited by a single feT^ale medusa

varies considerably. Jt is usually betweer twerty ar^ i thirty

five, Cn c-^e occasion an excenticnally large feiiale was tal:en

in the tow; her ovaries were seen to be cro-.^ded with eg?:s.

She v/as nut into a ser^arate dish of sea v/ater for the purpose

of counting the nu;rber of eggs thrt she v;ould lay. The

next morninp; at ^he hour the eggs were deposited; and the nu^-
/\

ber was found to be fifty-six, v/hich is/unusually large,
I made ^ any other counts but this was the only ti'-ie that
the number exceeded fifty, As a rule it is fro- tv/enty to
thirty-five, only rarely is it as high as fifty, fhese num-
bers seen reriarkably small when we consider the enormous
cuantit^f of eggs that are laid by many of the other ani-
mals of the ocean^ the number often reaching many millions,
as among so-^e of the Echirodermata and ;.iollusca.

It is a rather curious fact that these animals are

36

always so very regular in the ti-;e for leoositing their egJTS ,
v/hich is from fivo to six A. ;:. During the two sujixers that
I studied Turritoosis at the sea-shore, great nurrbers were
collected and ke'it in acuaria. On T-any occasions larose
early in the "orning to observe the act of spawning,- one
ti"ie they were watched through the en .ire night,- and always
the act of egg layincr was seen to oomnence at about five
o'cloc:: or a few minutes after. Very rarely did it take
olace as late as six o'clock; and on no occasion was the nhe-
noTenon observed more than a few minutes before 5 A, ivl.

Ihis Drecise periodicity is rot O'-l-ji confined to Tur-
ritorsis, but seeTs to be cuit^e prevalent arong the cedusae
in general. In Stcrr.otoca a icata. Stonotoca rugpsa and a
species of Ei|cheilpta I find that the eggs are deposited
also at a fixed hour, nar^ely, 5 to 5.30 A. I'. Professor
Broo::s found that Lirope and Eutina sr>awn at about S P. .M.
In Gonionema Perkins found the time to be fron 7 to G P. i.'..
Bunting found the neriod of dehiscence for Hydractinia to be
about 10 P. :... While ;..ere.ikowsky says that the eggs of

37

Obelia are laid early in the norning, etschnikoff also
Rives the tirr.e of snawninf; of 14 species.

Regular breeding habits have alsc been found to exist
among other r.arine anirr.als, and may be more general than
has been suspected. '';ilson in his v/orl: on the develcr-ent
of Renilla fo^nd that the eggs of that form were always
laid at about 6 A, M. In a single case only, he says, the
spawning took Place as early as 5,30 a-^d it was never oi)ser-
ved tc occur later then seven o'clock. The relagic Crustaceaij,
Lucifer Professor Brocks observed to denosit its eggs at 9 t:
10 F. M.

Bunting lound that by packing Hydractinia in ice and
keeping therr at a lower tenPBrature she v;as able to delay
the ti'-e of egg lading. On restoring the animals to the nor-
aial temperature, the eggs were laid after ?. short period
of time. Perkins fcund that the -'ieriodicity of spawning in
Gonionema is definitely ^ffected by charges of light. By
placing his --edusae in a dark place for an hour and then put-
ting the-T: in the daylight apparently normal egg lajring
again too'- place.

38

'..hile I did not try ex::eriments on Turrito^sis olther
with regard to temnerature or light, yet the changes of tem-
oprature from day to day had no noticeable effect on the time
at which they discharged their eggs, that ic, it occured at
thf sare hour or. warr days and cool, days. I^"" H^'b ^anner
the fact that the aquarium in v/hich the niedusae were contain-
ed was keDt before a lighted lamn all night had no effect,
on the tir.e of srav;ning the next r.orning, which took -nlace
at the fixed oeriod,

THE EGG.

The egg of Turritonsis is spherical and *» devoid of
a -ex.brane when first laid and none is subsecuently forned.
In size it is auito sn^all and can easily he oyorlool;ed. If
the water is free fro:^ sodirent and the dish containing the
eggs is placed upon a n)ace d)f black paner the eggs are vis-
ible to the naked eye. They -reasure .116 of a ir.illiTetPT
in diameter. They are aiiong the smaller of the medusae eggs.
:.ietschrikoff gives the measurements of the ova of nineteen

39

snecies of -ledusac; the sizes of which range from ,024 tti'^.
to 1,5 -.im. Cunina orobosr.idea ha>ada^ the smallest a'ld
Polyxenia albescens the lartrest egg of the species included
in his lot. The egg of Turri1;o"sis is ,iust slightly than
that of Rathkea fasciculata according to the ■^easurcent of
i.;etschril:off .

In the substance of the egg tv;c parts are distinguish-
able; an outer layer of cleareiY^ctoplasrr which consists
of viscid formative yolk conposed of protoplasm with veri
fine granules; and a central mass of e'^dorlas"' which is dense
and oraque end filled v/iih large, dark granules of nutri-
tive yolk. Fro- the fact thatfthe e-dorlasT is crowded with
these coarse dense granu^ies of nutritive naterial the egg
is very opaque and the ger-inal vesicle is not to be seen
frorr the exterior. Tlius the changes which take place dur-
ing maturation and fertilization, and the nuclear Phenom-
ena of segmentation, as well as the formation of the endo-
derm ca-Tiot be followed imhe living egg. For thislreason

40
the egfj of Turritonsis in not as nuitablp for study during
lifp as these beautinilly transnarpnt o.f^.f^s of Lirione and
Eutina for instancp, which allov; all the changes that take
place '.vithin Lhe egg during develoi-neri? to be follovved easily.

The soecific gravity of the eggs is greater than that
of sea-water and consequently they sink to the bottox of
the aquariuT, as soon as they are discharged froir, the cavity
of the urrbrella. In onacity Lhe egg of Turritc_sis is inter-
T-.ediate betv^een the egf^ oflStpniptoca rugpsa, which is extre~e-
ly dense and of aiohalky white color, and the egg of Stono-
toca an i cat a which is seni-transnarent and an^ears bluish-
white by reflected li^ht. In color the egg of Turritpnsis
is yellowish v.'hite.

MATURATIGii AI-ID FE.^TILIZATIO:..

Because of the opacity of the egg satisfactory obser-
va^ions on the nhenc-ena of rraturation and fertilization
are ir-'Ossible during life, excent for those changes v/hich

41
take Place on the outside. A few rinutes after the eg.^r is
laid the first Dolar body is niven off at the upper pole
of the egg. The second polar globule follov/s after a very-
short intervr.l. Thece structures are of an ephemeral nature
and soon disintegrate or pass out into ;-he water and are
lost. othing can be made out of their internal structure or
"fti^ of the arrangeTe^t of the chroiratin v«ith the lev/ nagni-
fication v;hioh one is obliged, to use in the study of :he livig
egg. However I was fortunate enough to get sectons of
the early stage.- of r)reserved eggs v/hich show the nolar bodies
in the ^rocess of being extruded. The ger-inal vesicle icves
to the periphery of thaegg, then a part ci its substance
is divided off and extruded as the first polar bcdy. In
Figure 7, whch is a section of an egg that was preserved
a few "inutes after it hai beer laid, the second nolar body
is iust being given off. It contains several granules of
chro:T;at,in scattered :.hrough its Glc^.w.r hy>iline .:ub.;t...:-cr .
Ir, oho ' , . little distance

42
fro" the pp,'^, but i:^ sti'l held in connL^ction •.;ith it by
so-^e -pans of attachnent, the "hro^iatin ha." co^ie topether

and for n :• single mass in the centre of the ^olar j^lob-

^ o

ule. The 'neans of attacr.ent of the r^lar bodies to the
^ 'N

Gurface of the egp is -^ot cuite clear, as the ep.^^ is desti-
tute of a •^e•■br^ne. It is r^ossible that so'-ie of the clear
liquid -^art of the ^roto^^lasr ray exude fro-- the substa'ice
of the egr as the rc'ar bodies are extruded ap.d be the "-eans
of holding the?r to the surface of the egg even during fixation,

As can be seen in the figure, the ger-^inal vesicle
during the extrusio" of the -polar bodies is i^ituate-i at the
very er.ge of the egf^j even, about hal:" of its bulk extends
beyond the general contour of the egg's surface. The yolk
granules are crov;ded around the nucleus with the s-^-e density
as in other narts of the e^p. After the second nolar body
has been given off, the ferale ^rcnucleus -eves back froT
the neriphery so-re distance. Here it is -let by the snern
nucleus a^d fusion of the two taV.es '^lace. V.hether there is

45
any definite snot for the entrance of the snerr-.atosoon or
not could not be decided. But I a- inclined to think thrt
the Tale ele-'^ent i.c capable of nenetratinp; the egp: at any
T^art; and that when it har once entered the substance of
the egp, the -ale and fe-ale pronuclei are brought to{?ethc.r
by the attraction existin.n; .tetwee-' the tv;o.

It was i-^nossible to see the discharge of the sriernato-
zoa fro- the nales; neither did I see then enter the egps.
And, as stated before, the eggs are so onaoue that the inter-
nal nhenoTiena of fertilization could not be followed i-i the
living snecimens. s**4 The -^e is reason to believe that the
sner~s are discharged at about the sa-^.e tire that the ferales
lay -uheir eggs. Fertilization talces nlace in the v/ater ir.-
r?ediatoly follov;ing '-aturation, and segr^entn.tio- begins in
a ver ^ short ti-e.

SEGMErlTATIOIi.

Segmentation is total and an-'-roxinately equal. V.hile
there is a slight difference in the size of the blasto-reres

at tiner. , yet this Siffero^ce is not const-rit and th'-y ?.ll
ho.ve. the zc.^e valu^ in develoT-enlj; that is, thoy are -not
divided in to macromeres and -nicroTeres, As** There is no
evidence either fro"^ observations of the livin,!7 egc^s, or
fro- the ntudy of sections of rreservpd Tiaterial that any
of :he blastomeres can be localised as forninp distinct
oarts of the future errbryo. During the first t-70 or three
cleavages the -rocess is usually cui$c regular , but beyond
the '"Ight cell stage the segnentatio^^ berores very irregular
and erratic; almost if not fully as ren^arhable as that de-
scribed and figured by Harritt for Pen]2?'li§ M^rlPlli^ and
of ;;hich he says; "Between the rxtremes of the en^bryoric
history fro"- the early cleavage to the forration of the
-orula are to be found the '^ost erratic and ancalous exhi-
bitions of develo- mental nhenoTe-a v;hioh have ever cone to
Tiy knovrledgo, if indeed its countermart has hitherto -"been
known. It is not strange that v;ith the -ic-tal Tnctures of
such sfady-going exhibitions as are found in the develon-
ment of annelids, -.olluscs, etc., one should regard such

45
Tonstrcsi ties as are very inr.decuo.tely rer^resented in the
various fi^urer: illustrating this ^j&^er as ab-^orrr.al to the
degree of beinp Dathalogi" ! And thus it seorredfto r?e vhen
first obs?rved; and as rointed out in the earlier raner,
the first batch of egfs v/ere discarded as having 'gone bad.' "

jVhen I first began the study of the develor.rnent of Turri-
tonisis . the irregularities of segmentation strucl: '-e as
very neculiar and I v/as at first inclined to thinl- that
they v;ere abnorrr.al. After I allov/ed the eggs tine to pro-
gress I discovered that they develored into nor-al r^lanulao
and thus was forced to conclude that this strange and irregu-
lar cleavage trust after all be normal for ihe snecies. On
several occasions the attention of a number of other obser-
vers ^7ho v/ere r/orking in the same Tiarine laboratory vas called
to "^.his nhenonenon, and they also exriresse'' surnriso a'ld re-
marked that thev had never seen segmentation nresentinf" such
a-^omalous and irregular features.

Iietschnikoff describes and gives a fev; figures of
a very si:'ilar condition of segmentation in Oceania armata.

46
He says: "Wenn bei dcr beschrieberien Weduser vr-rschiedene
Ab'.veichur.gen in der Zustandekcrren des viertp:^ i'urchur.gs-
sx.adium ccnstatirt v/erderi riiusster, , so konnte mar. doch bei
aller eine pev/isse r.egelmfts^ipkeit aufiirdfrj. Gaviz abv.-eich-
end in dieser Beziehung verhElt "i:?h Oceania armata, da
bei dieser ;;eduse die kattm ~dt einander vereinigter Blasto-
neren durchaus unregel-ftssig und ordnur.gslos nebeneinander

liegen. Das Abv;eichende in der .'.nbryonalentwickelung

der Oceania arxata hftrt roch richt so bald auf. Die Furchung
setzt sich in unregel'-;assigster V.'oise fort und fiihrt zuv
Bildung unfttr^licher Zellenhauf en , in derrn Innern inar eine
Furchungshtihle durchshii^mern sieht. Oft nehmen seiche
Embryonen eine ganz abenteurliche Gectalt an, deren Ursache
zum Theil darin liegt, dass sie sich durch Theilung ve.r:nehren,
Diesen Process habe ich an mehreren isolirten Blastula-
Stadie- beobachtet, so dass ich an dessen i-.xistenr nicht
zweifle." In Turritpisis, likev/ise, the latrr cleavages
take nlace in :: ront irregular -nanner and leac to the for-

mr.tior of r sharelpss ar.d grotesaue riass of blastOTores in
v/hich the cells are frequently held together very lO'-noly.
Tlie accorpanyinr drav.'ings unfortunately rer)re3ent only the
nost regular forms. This is due in part to the fact that
the very irregular forns v.-ere at first thought, as stated
before, to be abnornal; a-id partly because it v/as diffir.ult
to rake accurate carera sketches of these shapeless rasses
during life v/hile cleavages v/ere fciS^ r lace rather raridly.

'..hether these enbryos "ultinly by division, as .:etschni-
koff stated to be the case with Oceania ar^nata and to ;hich
he attributed in part Lhe caus: of their peculiar shapes,
I have no direct evidence; but thirk that it is very prob-
able that such may be the care, ts^ frecuer.tly the blasto-
mercs are separated into tv;o distinct masses t eld together
by a small isthmus of cells} even if they do not divide by
an internal activity, they must, occasionally at least, be
broken ar)ar^ by ^he action of the tides v/hen in the open ocean,
Several tires the experiment of dividing the egg during the

4g
comparatively early cleavages v/as tried a^d the parts were
four.d to cc'tirue their develorment ithout a;"y hindrance.
These experiirents v/ill')be described -ore in detail later.

Another -noint in v;hich the segmenting egg of Turriton-
sis differs fro;r thrt of Oceania arMJif- is that it does not
for:", a triie cleavage cavity. The blastomeres r.lv/ays forn a
nore or less rolid enbryo, as shov.'n in "he sections of hese
stages. Occasionally there are sr:all spaces left between
the rells; but a true segmentation cavity that later ferns
a blactocccle is 'ever for-"ed. In this respect also it is
siTilar to the develOTtraent of Pennaria tiarella as describe,
by Hargitt. As the coT.nletion of segmentation anrroaches,
these irregular masres of cells gradually trke .n a -rove
sy"-r:etrical fori;! and finally there is formed an oval enbryo
co-^pcsed of e solid nass of cells constituting a rrorula.

The first cleavage takes nlace about twenty to thirty
TTiinutes after the rclar bodies have been given of i . It
begins at the upner pole of the egg and passed down to ihe

49
Icv/rr rcle. Thus the e^,^, ir. divided reridionally into t;o
colic of arproxinatoly oGual size, When the division is com-
plete '.he blastomeres do not remain in close union, but
rove ar)art so that the tv.-o spheres are connected by only
sr^all arcs of their cirourr.ference. The nrotcrlas-^ic bridge,
v;hich frecuently occurs in hydroid egf^s at the lower pole
.iust previous to the ccpletion of the tv/o-cnlled stage,
is usually to be seen in the egg of this species; but, i^ is
much less conspicuous than is the case in Sto-Totoca. And
viher it occurs is less definite and clearly defined than is
the condition i'_Hydractiriia, as described and figured by
Bunting. Metschnikoff also figures a very beautiful ex-
ample of this prcto-las~ic ccni^ectio" in the egg of fausi,-
thoe marginata. In Turrito_;;^sis thepondition is nuch lilce
that of Rathkea fasciculata, as sh-v^n by the last -entioned
observer, in v/hich the con'^ections instead of becoming a
very definite bridge re-ain for a tine as a less clearly
outlined portion of the ectosarcal naterial. Proto- las-iic

50
currents nay be seei^. at tinos in these ':'onnectinp fila-
nentn. Their function does not seem to be clearly knov/n;
but it very nrcbably is conecte.: v/ith a read I'ust-ient of
the cytO'-las"i and the establish^-ent of an equilibrium^ be-
tween the different blasto-^eres.

Hargitt in his naoer on "The Early Develo'-^ent of
i^n.'ili^ tiarella" disoussos the occure-^ce of na-illae,
threads, a-^d bridges; c.r^cl reviev.'S briefly the observations
of a nuirber of other investigators in regard to these Phenom-
ena, and the ryto^lartic activities v;hich they have seen to
tal:e nlace in the eggs of a number of animals widely separ-
ated nornhol-gically. I:o definite conclusions are rea-hed
as to the functions of these various Phenomena, but it is
generally -.bought that ^.hey are concerne.i with fundamental
intrinsic changes within the cytonlasm.

These nrotonlasTiic connections are usually comnosed of
the ectosarc only. They are nresent -^ot only in the two-
celled stage, but. in several of the followintr stages as well
As the number of cells increases the :^cnnecting fil-s be-

51
coine less easily recoFj-iized.

The second cle:nvage occurs r.bout tv/e'^ty-i'ive or "thirty
rai-iut?s after the first. The -lane of division is also
meridional and at right angles to the first seg-.entation.
It begins =^* to the centre of the egg next to the furrow of
the first cleavage and slowly extends out toward the neri-
phery. "hen the division the four blastoireres
u-dergc a slight rotation froT righ'u to left; a^d i'^ the
centre of the egg betv/een the cells there is^ at tir.es^ to be
seen a srr.all onen s- ace or seg-.entation cavity v/hich -^.ay
extend through the entire egg as shov;n in Figure 12.

After a lanse of tine ecual to that v.-hah occurs between
the first and second divisions, the third cleavage furrov;
arrears. This nlano of division is equatorial and divides
the egg into eight blasto-eres. ihen the sf:gnentation is
first coTT^nleted t-he two ouartets of cells are' situated one
upon the other and forr a ''ore or less s'^herical v/hole,
as is the usual arrangement in eggs in which segi^u-ntatioh

52
is equal and rr.f^iilar. This arranpe^e-^t of the blastoT^pres ,

hov/ever, is of very short duration, for soon a separation

ce
takes nla* betv/een the cells of the lov;er quartet and

two of therr, roll away fro the olan^^ of separation in one
direction; the other two Tovinc^ out in the onoosite direc-
tion. In this -i^ration the blastorreres "ove throuPh an
angle of 45 dep:rpes or ^ore, and finally co-e to lie in
such a -position as to forii; a semicircular nlate as shov/n
in Figures 13 and 14. The ser^aration and rotation of the
cells of one quartet seeTis to be constant in its occurence;
but the final arrangement of the blastomeres is not always
as rep:ular and definite as that shov/n ii the figures. At
tiS'es they are rr.ore loosely a-^d irregularly connected, and
may assume rela'ive "ositions si'-ilar to that shown by
Lletschnilroff for Oceania armata in Figure 34, Plate 1, of
his "Embryologische Studinn." In the case referre' to the
blastomeres are ?.o srtroa.' out that the individuals, with
three exceptions, touch only one of their fellows, thus

53

resenblin.rr a r>trinp If beads soTewhat coiled,

V.ith this seraration a-d rollinp ar-art, the rrp:ularity
of arranger-pnt of the cells in the seg^entinfT egg is lost, and
the stager, frc" this noint on become '^ore and more irregular
v/ith each successive division u^ to the time when the re-
ad.iustinent tal;es -ilace v;hich is the beginning of the fnr-
nation of the free-sv/irr?ing e-: bryo.

It is possible t-- distinguish, during these early
cleavage stages, a layer of ectosarc around each individual
blastomere. Later as the cells increase iri nuTber and be-
come smaller, the ectcsarc covering beco-r-es less "O'^soicu-
ous and finally is lost frcr sight entirely.

After a"" interval of about one half an hour, the fourth
segmentation begins. The divisions of the different cells
no longer tahe nlace sirultaneously; sere occur a few minutes
before others, but all are cornle'ued within a coTDaratively
short tin:e. So&'ar a- the cleavage itself is concerned, it
is ntill ecual and regular, but the arrangement of the blasto-
Tieres is no longer regular or definite. They annarertl>

54

follov; no lav; of syrrnrtry, and T,ay coT:e. to lie in any nosit-
io-i. Figures IS, 16 and 17 shov; throe diffe:-ent forms
which the cells of the sixteen cell sta^e accuire, and
various other arran.c^e^ie-ts of the blastOTieres v;ere seen v/hile
studyi"? the livinp: eggs v/hich could not be figured for
wa-^t of snace. However the three figures are sufficient
to sho',7 that the general forrr, of the egg in this stage T.ay be
very different. In Figure 15 it is nossible to i-iagine a
direct relationshin to a nreceding for^- ,iust a little -lore
irrec^ular than is sho'.?^ in Figure 14. In a for-' as represen-
ted in Figure 16 the descent of the different cells frorii
the individual bla3t:"'eres of the eight cell stage is less
easily rccogrized. Firure 17 sht)Y,'S an egg in v.-hich all six-
teen blastomeres are spread out to frrir. a flat plate one
cell thiol; in the forr of a quadrangle, Cne can easily
conceive hov; this arrangement can have resulted frcni a
regular eight cell ::tage in vhich the rotation of the cells
of the one quartet vas greater thar that shcvn in Figure

15. The flat, ST^rend out -osition of the cells nt once
suggests the idea thit the eg?^ "lay have been subjected to
nressure, -ted This r^ight have been the case if the eggs
had been studied on a slide under a cover glassj but there
is no evidence that pressure was the cause of this nlate-
lil:e arrange'-ent , for these forrs v/ere occasionally found
arcng a variety of othe- forir.s '.vhile studying the living eggs
in a sr-all preraratior dish in sea-vater with a two-thirds
ob.iective. As the eggs nresent a number of different forms
when subjected to the same external ■onditions, it see-s
that the cause of these differences rust be sought in the
nature of the egg itself rather than in any surrounding
influences .

The later cleavages follov; at intervals of about the
saT:e duration as in the ^receding stagjes. The irregularities
of arrangement of the blastoreres increase as the cells be-
cone riore numerous. On account of the smallness of the
blastomeres and the extreme ODacity of the oPf,, it becomes
imnossible to follow the segmentation in detail a-^y further.

56

Figures 18 - 21 sho;v a few of the latnr stages of co^nDar-
ativoly very regular for:iis. Figure 20 reriresents an egg in
which the blastomeres are arranged in tv/o ^rain grouris held
together by ajnarrow isthmus of only one cell in thickness.
Some eggs were separated into three or four thickened clus-
ters that vrere .I'oined tbgether by small nasses of conner-t-
ing cells. In others there were smaller grou'DS of blasto-
meres nrojecting out fro- the general r.ass of cells, thus
giving the './hole sonev/hat of an a'neboid ar»r)earance. The
tern; amoeba-like seens to lost clearly represent the shane
which soTe of these late segmentation stages assume, for
if a simDle outline of these remarkable a^^d grotesque forms
is drawn it has a general resemblance to an a-^oeba with thic!:
blunt nseudonods, V.'hether these irregularities in the sbape
of the egg during late segmentation, and tie tendency of
the cells to arrange the-^selves into '-ore or less distinct
lobes is 'lue to an amoeboid proT^erty of the cytonlasr of
the egg, or to a tondoncy to multiply by division during
cleavage, as was suggested by iMetschnikoff fcr Oceania ar-

57

mata. there is not sufficient evidence to decide. It may
be r'ossible that both of these factors act ir, deterr-inin^ the
shar^e of the segienting -lass of cells. And doubtless the
metibraneless character of the ejy.c^ nlays a -art in thene
phenomena

PLANULA.

V/hen segmentation is coTdete a solid efrbryo is forr.ed
v^hich r.ay at first be called a ncrula. Small snaoes occur
soroeti'-es between the blastcneres during the di^fferent
cleavage stages, but they are sooner or later obliterated
by the crov/ding together of the cells, A central cleavage
cavity v/hich is later transformed into a blastocoele is not
forred; consequently a true blastula does not exist in
the development of Turritcnsis, In this resnect it differs
very "-arl^edly from Stor^otoca and the majority of hydro-
medusae of which the develonment has been studied, in
which a definite blastocoele is formed that becomes filled

58

finally v/ith the -ri^ratinr endodprrr cells. Wher the develOD-
in.r Pf^g is r.bout six tc eight hours old, the very irreg-
ular sharDe, which the seg:renting rass has assumed, becomes
less marked. Gradually the cells becore rearranged; the
lobes a-^d processes which rreviously were so conspicuous
are now drav/n into the nain mass of cells, and the egg is
transformed into an oval e-bryo. This ^Fccecs of rounding
uri lasts fro-- two to four hours. The cells of the erbryo
now develori cilia, and the larva begins to rove. At first
the riovements are feeble, but soon the larva is able to
leave the bottor. of the aquariun and svar, free in the water.
Eggs that are laid at five to six o'clock in the norning
develop to the free-swir.r,ing stage by four in the afternoon.
The larva sv/ins with its broad end forv/ard! and has v.
snaal or cork-screw notion, which proreis it onv/ard.
This "lethod of swinning is con^on tc hydroid larvae. When
the embryo reaches this stage the cells become very nuir.er-
o~us and snail. And before the cilia are developed and

59

T.ovement begins it rese'-bles an unsegr.entod egg vory nuoh,
except that instead of being snherical it is nov/ oval.
In si.";e it is about the sa~e as the unsegr.ented egg, if
anything rather sr.aller. The decrease in size "ust be ac-
counted for by the fact that scrr^e of the yelk has been di-
gested; and the larva evidently has - ot yet acouired any
means of receiving food .fro::i the external world.

The larva rer.ains i- this oval conditio:- for soine
hours, after v;hich it elongates to form a tyoical "lanula.
I'/hen the embryo is twenty-four hours old it lengthens out and
becomes more slender and assumes a general aDpearance as shovm
in Figure 23, As it becomes older it grows still longer,
figure 24 shows a larva of thirty hours. It has now the
power of c^ntra-tion; and is sensitive to stiuli. When
the cilia a.e first developed and for some time during the
oval condition of the larva it swims near the botto- of
the aquarium. But as it grows longer and elongates it rises
in the water and s'.vi:,s at or near the surface. The length

60
of tme durinc: which the evbryo remains in the free-swim-
niing planula stage is variable; but as a rule by the ti-:Te it
is about forty-eight hours old, it begins to sink tov;ard
the botto.- of the aquariun^, and to svini less rapidly. After
the sniral sv;iir,rr.ing rriovements are lost, zhc wlanula is
capable of gliding along the bcttoir. of the dish for some
time. Finally the notion ceases altogether and the larva loses
its cilia and is ready for ::ttach:ient. This stage of de-
velopment is reached under favorable conditions about forty-
eight to fifty hours after the eggs have been laid.

The rlanula is very opaque, and thus it is i-mossible
to rriake out anything about its internal structure in study-
ing the living forr^.s. Specimens in various stages oi de-
velonr.ent were preserved and sectioned for the study of
cellular structure. The descriDton of this structure v;ill
be given in connection with the forration of the ger- layers.

Brooks describes and figures an ectodernr.al invagination

61

at the posterior- end of the planula, lie :;ays: "In :i living
olanula it is easy to :nake out the posterior end, an ecto-
dernial invap^ination , which looks vory T.uch like the :Toiith
of an invagiiiation gastrula, but this resemblance is mislead-
ing, for the careful study of a sirdlar structure in the
planula of Eutina shows that the invagination has no con-
nection vath the digestive cavity, but is an ectoderteal

gland for the attachment of the planula." From my observatioa

e

I am forced to regard this struture, which he describes,

as a variatior; rather thar a normal feature. It seems to be
an abnormal occurence v/hich is found only rarely. Among
the many specimens wh''ch I studied both in life and from
preserved material, such an invagination was met ■.ith only
on one occasion. Then it v/as at the anterior end of .the
Planula instead of the posterior. These f ej-turas nre clear-
ly abnormal features of the developing Turritorsis
Planula.

62

EXPERIiviEI^TAL.
The very irrogular character of the segmenting egg and
the loose connecLio'- of the blastomeres; and their ten-
dency to separate irto nore or less definite lobes and nro-
tuberancfs, as has been described in the section on segmen-
tation suggested the nrobleT: What would be ohejeffect of
dividing the eggs during the ccn-.Darativoly early stages of
cleavage? V.ith chis questior in mind a few experiments were
tried. The eggs v;ere divided during several stages of seg-
mentation. The best method for separating the cells was
3'cund to be by placing their, or a clean glass olate moist-
ened with sea-water. Then with a finely ':ointed£eedle
or -viuh a very delicate scalrel the blastOmeres cculd be cut
or torn ai;art without being crushed. After they were divided,
they were flooded frox the glass nlate by water from a
pi-iette into a dish of sea-water and watched in Lheir develc-^-
ment. The advantage of separating the e.ggs on a glass nlate
is that they are held slightly by surface tensio- , ^.-■'^. :o

63

r.ot rotate as readily v/hile br-inf{ cut avart, i.ggs v/ere di-
vided during different sta?;es of cleavage from tv.-o lo six
hours old. They were then olaced under conditions as near-
ly like those under which the eggs noo divided developed as
possible. Jniortunately , as these experinients were inci-
dental and inccirplete, no eggs were divided during the
two-cell stage and their cleavage followed in detail,
So;:.e eggs that were laid between five and six in the if^orn-
ing were divided at 10,46 A« ii, iiore than one half of the
frag.T-ents continued Lo cevelon and by six o'clocl: in the
evening had reached the free-swimiting stage. They were re-
tarded a little in their development; whole eggs usually
arrive at this stage at about four to four-thirty. They
were slightly smaller than einbryos frori whole eggs, but
annarently lust as active and norir^al. except in size. By
the next -corning .hey had reached Lhe elongated planula
stage and were in good condition, swirrr.ing at the surface
of the water.

64

At another time 3o::e younger eggs were divided. These
shov;e^', practically the sar-.e results in develornent. The
opacity of these embryos vrade the study of their ir.inute
structure ir-ossible during life; and because of scarcity of
material none rculd be r-reserved to study their histology
fro~ sections. Hov.-ever these few inco-ii^lete experiments
shov/ that fra-p.ients of the egg of Turritorsis are canable
of developing into ao::arently entire and normal embryos of
slightly smaller size,

Hargit-. artificially divided some Pennaria eggs dur-
ing the first cleavage and figures a number of resulting
segmentation stages, v/hich « very similar to th«l*of whole
eggs. He cays: "As v/ill be seen, each of the resulting
halves behaved In a manner indistinguishable from thai of
normal eggs. These half e- bryos were followed through the
entire orocess of cleavage and Lhrcugh the later reta-
morphoses into planula and olyp, and in every resT^ect,

65

size alone oxcepted, the i^rocess was nerfectly normal."

To my krcwledge Haeckol was the first lc rublish the
statement that halves of hydro-,edusa egps would develop) into
norr.al eiribryos. For sor.e time naturalists in general v/ere
inclined lo doubt the fact^ but since the work of Boveri,
Hertwir brothers, Roux, Driesch, Viilscn, Korgan, Loeb and
others on the fragments of eggs, the development of ei^ibryos ,
abnormal and normal, from the portions of eggs is a question
no longer to be doubted.

FORMATIOi: OF THE ECTODERM.

In ihe develCvH-.e-it of the egg of Turr iter sis the ger-
minal layers are not differentiated by process of eribole,
delamination or cellular ingression. During segmentation
the blastoreres do nrt separate and arrange themselves around
a segmentation cavity which later is transformed into a
b^a-stocoele. Thus instead of having fcr-ed a coeloblastula,
we find that cleavage results in the formation of a solid

06

cvr.l embryo destitiito of n Mr.stocoelr , v-hi<"h rc.y be cr.llPd
r. noriila strpr. The cells of the sep-'-ertinp epr are all
alike ir^ ctriicture and nearly equal in size; so that they are
not disti- ruishable into r^ri'itive ectoder- and Tinitive
endoder:-, vrhich ir. the car.e in fcrrs v;hero a definite de-
lariration takes rlace, as is so beautifully shov/n in
Liriore and Gerypnia, and in sneeios where cellular inf^res-
sion occurs as in Stprctcca and Clytia for exa-nle. Fir-
ure? ?5 to 50 illustrate the u-ifor-ity of the cells, ard
the solid character of the efP. curinp seprentatio:- . In
I'ipure 27 a sDace exists between the blastcreres near ere
end of the epp , but this is not to be regarded ar a true
cleavage cavity. The next figure shows three of these false
cleavage cavities. They occur only cccasiorally. As
stated before rost of the epps are entirely rclid.

About the tire the irregular rass of seg^entinp blasto-
neres is retarcrnhcsed into the oval rrrbryc, the cell boun-
daries are lest for a short tire and a syncytiur is f erred.
This syncytial structure ir crowded with yolk pranules and

67

a ruirber of nuclei are scattered through the protrrlac::. The
•nuclei soon brcoine rove nimorous near the periphery; ard
ther cell v/alls bepin tc arrear ar rhovn ir Fif:ure 33. Tliese
cells are tc becor^e the ectodern, v.OiichjiE socr separated
fro^ the inner structureless rass by the development of the
iresof^lcea. Vo\; the ectodern^ forrs a distinct layer, ccr-
pcsed cf cclur^nar cells all of which are at first sir-ilar
i-^ structure and lie parallel to each other as shewn in
Figure 34. The differentiation of the ectodern cells takes
Place later.

The forraticn of the ^er^inal layers i^ I^rj'ij-f^r^is
is different fro--- that which has penerally been described
for the developrent of Hydromedusaf , Ir the na.iority of
forr-s previously studied the differentiation took place either
by delarinat: on cr by cellular inpressicn, unipolar or rult--*
pclcr. These rethcds hove been well described and figured
by I/etsch^il'Off for a nuirber of species.

Ir Aplaura ard rhcpalcnera there is found, accordinr to
letschril'off , a solid so-called rcrula staf^e destitute

of clor.vnf.c cavity, thr r.ur.erf icial crlln of which nro con-
vrrtrd irto thr ectodrrral layer, vrhilr those within re-
present the endodern. Here thf t;\'0 layers ere forred direct-
ly v.-ithout the fcrratior of a syncytial structure,

Ir Eudendriur and Fenrar.ia acccrdirp tr Harritt's
descri-^-tior a condition screwhat si'-ilar tc thnt of Turri-
t ops is is found. He says: "Indeed ir both FudendriuTr and
Perraria, not tc rention other cases, cleavage v^ould
seer to result primarily in the fcr-ation of a rcre or less
characteristic syncytiun^, the subsecuent develerrert of the
perr layers tr.l:inf r]ace by a gradual differentiation of the
syncytial elererts, first ard naturally the ectcderr, and
later, often very '■'uch later, the enuoder-."

The syncytia ijcharacter in Turritc-sis is acquired
under favorable conditions, whe- the cnbryo is about six
hours old; at the •'. i"-e that the irrcf^ular rass of ser-
rfntinn cells is retaromhosed in to the oval embryo. And
I a- inclined to thin'- that the for-ation of the syncytium

69

ard the '^harP'e of shn-^e of the dovplrrinr r'-bryc rre -^on-
rertcd •hcnorcna. The length of tire diirirp v;hirh thit: con-
dition IrvEtr ir> evidently cr^rr,ratively r.hort, for noon
cilia develor and the larva be.Pinr; to r.rvir. ^Stft Mean'"hilo
the rerirheral refTion of the cyncytiiin has been trancforred
into a distinct layer of ectoderral cells, se^arrted frc" the
inner rass cf tissue, etill rtrMrtin-eless ir character, by
the develorrent of the i^esoplcea.

Frc- the fact that a syncytiu'^^ or rlas'-Ddiuit-lil'e
stmicture in for-ed, it is irrorsible to localize a-y of
the blastcreres cf the segr^ertinr ppr- ^vhich will for^- snecial
narts of the future embryo. Ever those cells v.-hich are at
the surface at the cr-rletion of serre^tatior car'-ot be
reparded as ^riritive ectoderm-, for i*' the brea--inp dov;n of
the cell boundaries, the forrration of the syncytiun, and the
recastinr of the cells it is quite ir^'^ossible to say '"hat
charpe cf the -protc-lasr ray take ■^lace.

70
FCFr'ATIOr CF 7HF FrDCDERi:.

The forT.tior of the p-^dor'err- ir Turritorsis carrot
be -dsTted to any of the sche-es of the develo'i^cr.t of the
Hydro-edusae rhich have "beer sketched by '■etrchr.il'cff ,
He dint irruishes three Tinciral rp+hcds for the develor-r
rent cf the inner rerr layer: First, delarination , a
rrccers: ir rhich the i^e.cfert^'np blastc-eres divide in a
plane nearly parallel to the rurface; and the inner rarts
or cells be'^ore -^ri-itive erdoderr^, vhile the outer rarts
rerain as rriritive ectoder-. Second, '-iilti'^'r^lar inpres-
sior, i-" "hich cells riprate i^to the blastoccele fro" dif-
ferent regions of the rerinheral cell layer, a-d ere trans-
ferred irtr e'doder^al tissue directlv. Of this '-ode he
describes seve-^al subordinate types. Third^ u'^inolar "i-
pration, similar to the '-■recedinp exce-nt that the ':ri'^i-
tive endoderr cells are piven off at one pole only; at
the 'posterior end oT the larva.

In Tiirri-opsir the e'-dodern is derived fro-^ the syn-

oytial nasr of tissue left i'^ the re^-tre r^f i]-xe e-hryo
after the eetoderr has been forred ard nerarated off by
the develo-nert of the -pGr^loea. The irrer perr layer
as a rule is for~ed -uch later thar, the ectcderr. Soon
after the simcrtinp '-e'^brrre is developed cell bourdaries
be.fin to a-^r^ear in the syneytiun in the i-^terior of the larva.
The cells thus forned are ririritive endcderral cells, and
are crowded together without any defirite arranre^ent for
a nurber of hours. Stares ir. -hich the cell vrallr. are rean-
r>earinp are shown ir Figures 34 to 36, V.hen the enbryo
is about forty-eirht to sixty he\jrc old, the tlr-e at which
attachment takes nlace, a fissure a^'^ears i" the -^iddle
of the ^ass of endoder'-al tissue. This is the befinninp
of the ccelenteric cavity. This separation begins near
the anterior nart and rrcws toward the rosterior end. The
coelenteron f^rndually increases in size, and at the sane
tine the e'-doderrai cells b'-pin tc be rearranged; and fin-
ally becore situated narallel to each other with their baser

72

oprinst the -osoplopa nnrl forin a dofinito innrr prrr l^ypr.

Gerr! has obsorver'' ir> Roiifnirivillia that (hirinp the
course of cell niltir-lication the cell hourdaries br—
core ir.distinct a?d thc-t the -^eri-heral r.rd certral ruclel
are nltrrether identical. But this s'-ecies differs frcr
Turritcrsis. rcccrdirp to his descrlTtior ir the fornation
of the corract roriila stare, ir that it is brcuf^ht abrut
by r; nultirolar ripraticr of cells into the interior of the
coeloblastula; v:hile ir Turritprsis the rorula stape results
directly frcr se.c:nertation \;itho\it any reco.rnirable rigration
of cells.

The fcr'^aticr of the erdoderr ir Turritcrsis there-
fore differs fro- nearly all the -'Cthods v-hich have nrevious-
ly beer dercribed; ard v,'hich in the rain conforr to one or
another of the sterertyred rethodr as established by i.'etschnl-
koff. The nearest arrrcach is that^described by
Harritt for Zuderdriun ard Pennaria, in vhich there is also
rore or less of a syncytium for"-ed nrior to the differertj-

75

ation of the gerr layerr.

CELL I.;ULTIFLICATION.

DurinfT the er.rly cler.vr.pe rhasec 1 ho crlls rultir-ly
entirely by the procosE of ritosic. But i" the later rhasec,
esT^ecially vhen the egE is a-;:'ircachirg that r.tape in ';;hich
the cell l^cunclaries are lost, there is f^ord evidence that
direct cell divisicr ic aire ef freciient occurence. In this
reriod of develorrent ritosis and aritcsic take rlace sirul-
tanecusly i^ the different cells of the sep^-entinn cf,F.» -"icr-
iire 31a shov.'S a karyol-inetic s-:irdle in the •,ietar)ha:- ;
jij-;ure 31^ one ir\ the a-^a-r-'hase. The chrorcscr^es are larne
ard nroni-ert; but are toe closely rrrrded topether to be
cour-tfd • ith accurrcy.

The nuclei v.'h^ch divide aritoticelly vary in si:!;e con-
siderably, ar^d havp a reticular a^'^earance. Fifur^ 3?a
shows a larr^ rucleur of this reticular chrracter vnth the
chroratin scattered rbcut in the lirin nrrhrorl:. Firures

Sfb to 72e il?.u?trp.tr riirirl in vn.rionc rtr-rop of a'"itntic
division, rrerue'-tly ir oollr. vhere^'^itorAz takes ■^'^r.ce
nr'^y of the yell- frro-^ules hove been ripester! end r-onse-
ciiertly are ferer thar^ in cells v.-here dir:eEtio- is less
active. It ray be that the r.orr active functions of dipes-
tior and the rhenc-era of direct cell divisic^ are associated
v.'ith each other. Tr it ray be that the vie- of Flerrinp and
Ziep:ler, that amitosis is connected viiVn a hiph S'^ecial-
ir.ation of the cell or is the foreriin'^er of dep:eneration, ar-
nlies i-" this case. This latter conception sec-s nlaus-
able, fcr v;e find aritosis to be r^ost abundant shortly
before the cell bou!"dariesrJsar»'^ear a^d 'he enbryo is
transformed into the syncytiur.

For a nurber of years it has been lrnor;n that anitosis
is cordon i- follicle cells, digestive epithelial cells,
su'D^ortinr' cells, etc.: but generally it was -ot su'r^'^csed
to take riace in early e-bryonic develor>-ent, V.'ithi- the last
fe'v years however a number of observers have discovered this

75

phepcmenop ir the devplorrental stares nf various for'-s,

ATTACH' -EFT .

Ur^der favorable ror^ditiors vrhen the larva is about
fifty hours ''Id it rracher that starre of develor'-ert nt
v;hich attaohrert tnkec •nlace. In -".re^^aration for this pro-
cess the rilanula settles to the botto", loses its oilia
and consecue'^tly its rovere'':ts cease. The "-anper of attach-
inent in Turrjtorsis lil'e that of Stp-iotoca differs frcr
that usually described in hydroid develcr-nent. Instead of
settlinr de:7n o'- the rnterior end of the '^lanula accord
to the rethod which occurs in Eude^driur , and which has
bee'- repardec as tyical and used in descriT'tions of the
e-bryolcpy of the Hydrcedusae in text-bcclTS , the rlanula
becomes attached on its side by nearly its wh'^le lenfth^
and is transformed into a root. The hydranth instead of
rrowinp u-^ fro- th'^ -^osterior e-d of the nlanula as in
fcrTS V'hich attach th^rselves by the anterior end, de-

li nr

76
vpIods frci^ apud tho.t is pivF*' off frr^^ thp rft, 'irurl ly
nbcut thF '-iddlp.

T-Tcfer:SCT Brcckr, observed the fr-ct *h?.t the ■^larula
is transferred intr a ro^t in Turritor^sis , Futira a-d
Hydraftinia; and pives a brief acccTt of the sar^e ir his
raT}er cr "The llfe-Histcry of Eutira" doc''- ) . l'etschnil;off
describes P'^d fipures fcr I'itrojccra the fact that the larva
beconies attached by its side and is almost v.'helly c-lcyed
ir the fcrratirn of the hydrcrhiza, v:hile the first hydranth
prrev;s out of it by a kind of buddin?' (Erbryclorische
Stndien, lf^86).

In general the attachrent of the Dlanula is sirilar
in Tyrriic^sis to the rethod vhich is followed by StOTCtpca,
but the fcr'^er does rot t?orrorly produce secondary hydrc-
rhiza. In Stojotpca about the tine the hydranth bud a^^'^eers,
cr ever- be^>re, the rcct branches rr'vlrr rise usually to one
or tv'o secondary roots; In Turritonsis this branchirr rarely
tal-.es nlace, at least r'urinp the first fev; days of the de-

77
vplornert of the hydrcrth.

Professor BrcclT. ciosrribcs r.nd fif^uroc i^ tho rlr.rnla
of Eutira an octodornal adhesive flared. It oocurs after
the endoderr. a'^d the digestive cavity are f or'^ed , ard l^efore
the a-n-earance of the ^outh, as ap ectoderra" inva.Pinati on
at the sDall e-d of the -tlanula. In Tiirritojsis no such
special ojtan of attachrert in found. The larva rrrbably
beco'^es fixed by a secretior extruded frc^ the eetoderr.
cells alonp the v;hole lenj^th of itr, body.

DEVELCFFEKT CF TKF HYDFAI'TH.

Shortly after the Ir.rva becor.es attached a bud re\o'[o^'!>,
usually at about the co'-tre of the root, rhich is the begir-
^inF of the first hydra'^th. Four si-all nrc.iectirris ar-^ear
early arourd the distal '-art of th*-' bud; these rin later
forr the first circle of te-tacles. At this ti-e nc -outh
has yet developed. /Jyourr rolyr i- this stape of develon-
Fert is rhov"- i'^ Tirme 37. The hydra-th bud rertirues to
pre- tallrr arc aftfr a fe- hours r seccrd rhorl of ter-

78
taculrr budc^ is forrod pcpp dirtanop holov; the flrr=t circlo
of tentacles. Vhe^ the rolyr ir frc tworty to tvp^ty-four
hoiirr. old, or about -t^werty-ti-o hourr ai'ter thp opp ic laid,
it iE roady to devolor thPXhird vhorl of trptaclpr:. Thus
thp tpntaclpc r.earPEt thP ariox of tho hydrarth arp thp oldprt
ard larppst. Thr circloc arp irdofirito, that ir, tho ton-
taclpr of a v/horl do rot all aris; frcr the srrp ]pvp1; so
that ir tho advarcrd hydr^/^ thry havp rathor tho ajjppararop
of hpinr scattorpd thar arrarprd ir rlrclpr. Thp tortaolps
v/hpr fully dovplcrod arp stout a'^d filiforr; a^d aro carable
of 'uch Pxtr?ision and ccntractior . Firurps 37 to ''^1 illustrafe
varlour staror i'-' tho parly dovplorrrrrt cf tho hydrarth; thP
you'^FPst bfirr about fifty hours ard tho '^cst raturpd scr-p
sevp-'ty hours old, Fif!urp 3? shcv.'s a forr irfvhich tho ^rlyr
arises frc- rear tho prd of tho hydrorhira. This is oxc-pt-
ior.al. A hydra-^th •.vith thp third rirclp ci tortaclrs is
shorr ir Fifurp 41; the tprtaclps of tho first v.-horl havp
bpco-^e corsidorably Plonpatpd, The hydrooaulus row boccrps
Irnppr ard Tcrr- slprdpr; ard thp hydra-^th assuTPs a fusi-

79

fcrr body.

The ^r'yrs that I rrrrod fron PKrs r-.t the af^r of throe
days rere ir the '^ain features like the hydrarths of the
adult rrlory found and fipurrd by Profecr,or Brooks, ex-
cert that they had rot yet c'^volored as rary trrtaoles. In
his desrrirtio-^ he f^nys: "The u^ri.r'ht stems of "-he hydra,
fron 8 nn, to 12 if^. high, bore large terninal hy''ranths ,
as v,-ell ar <^^aller oner v;hich v/ere scattered irregularly
along the ster nn short stalks. The Irng fusifrrr bcdy of
the hydranth carries frc^ eightee-^ to twe-ity thic"', short,
filiforr tentacles, which are arranged in three or rore
indefi-itr rhorls. The redusa buds originate around the
ster .iust belov.' the hydra'^ths , and they are themselves car-
ried 0- short rters. The nerisarc is rot annulated, and
it forrs a loose cylirdrival sheath around the i-ain sto^-,
and the short branches v;hich carry the lateral hydranths
and the younf r-edusae, v/hile the latter are invested by a

80
ruoh thinnrr fi.nd rorr trrrf-rarrrt crpcule of rierirr.rc. The
f^hrath C" thr pte" is thirl- rnd crurtrd vath fcrripr rattrr.
It trrr^'rr.trE f.brnrtly by r. rharn cr]]ar ,1u?t bflcv; each
hydranth. The younr hycranthr ard the f^rducae are biidded off
above the collar, but they soon becce entirely sheathed
ir rerisarc by the prcvth of the ?ten-. The vs-lc yellcv.-ish-
red hydranths are very sirilar to those of Tubvj.aria (All-
nan) and the hydr^^jdd is so sirilar to Dendrcclava Dchrn:". i
recently described by Veisnam), that they nndoubtedly be-
lonr to the srre prnus."

SU'^APY.

1. The ova of Turritrr sis arise ir the ectoderr- of the
Faniibriur, They' prcv; by the absorrtion of the rriritive
ovaria:- cells; and vhen "ature are densely crov/ded with
larf:e yell: rranules.

2. Dehiscence takes ^^lace at a definite tire, frcr
five to six c'clrcl: i'- the r-orninf;.

3. The epp is srhericcl and -e'~branel"ess . It is cor-

01
rospd of r.'" outer Ir.yor of riearor pctorlasn arcl a rrrtral
narp of ordorlas- v;hich is d' nso and 0"naqup and fillrd ivith
larne, darl: yo].',- r' heron.

4.:NfatTiratior' and f ertiliration talre rlace in the viator
after the epps are de-nosited. It ir. i'-rrj-r-lble to r-ake
out cetailn in the livinr eppc because of their o-^aoity.

5. Cleavage is total and rearly ecual. Ihe first thrcr
divisions are fairly regular; hut during the later
spgrentatior the arrargerent of the blastcreres beror.es very
irregular and erratic. At the ccr-nlet\tion .cf .segmentation a
solid rrrula rtage is f erred, i?^ rhich the cell boundaries
are lost for a tine giving rise to a syncytiur.

6. Farts of eggs whirh are d-ivtd^ during the cleavage
stages continue to develor ard from larvae which are ncrral
in every respect except size,

7. The ectc(''err is forred by the rean^earance of cell
walls in the perinhery of the syrcytiu" '-ass; and is seppratec
fro- the interior nart by the fcrTation of the Tesogloea.

82

8. The forr-atior of the epdoderm follows rore of the
tjT'icrl rethcds described by etschr^Koff. It arises late
in the larval life fror thr r.ynrytial T^ass of tissue left
i- the interi'^r of the e-bryc after the ser.aration of the
ectoderr by resc^lcea. Vhen the cells first reai^rear

they are crcv;ded together without any '-"efi^ite arrangerert ;
finally hey con-e to forir the distinct endcder-al layer,

9. During the late segrentaticn there is evidence
that soTC of the nuclei divide aTitctically.

10. The rianula beccres attached on the side by nearly
its entire length, ard is transfer'^ ed into a roct.

11. Ihe first hydranth develops fro-- a bud which is given
off at about the riddle of the root socr after attachre^t.

12. The tentacles develop ir^ indefinite whcrls. Fach
whrrl has four tentacles. The oldest are nerrest the distal
end. In the fully developed hydra- th they have the ar-ear-
a-'ce of being scattered rather tha- being arranged in circles.

83
LITERATURE.
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of U. S. A. Part IV. Hydrcldae.
1865, Apassin, A. r orth Americrr Acaler^hae. Catalrf^ue of
the yus. CoTTD. Zocl. Part II.
1900. Allen, C. ;v:. The Develon-^e-'t of Tubularia ''rocpa. Bid.

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1872. All:^an, J. G. A 'ionopranh of the Gymnoblastic Tubularian

Hydriods. Ray Society .Lerdon.
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Wiss. Zool. LII.
1891. Erauer, A. Uber di? Entstehu-ir^ der Geschlochti^-nrodukte

und die Entwickelunr-^ von Tubularia ness'-ibranthe'^m. Id.
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Studies frcT the Biol. Lab. Johns Hopkins U-^iv. Vol. II.
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84

1886. Brooks, W. K, The life-History of "ohe Hydro.'^.edusae,

Boston Soc. of l^at. Hist,
1890. Brooks, W, K, The Life-History of EDenthesis McCradyi.

Studies fro- Lhe Bioi. Lab. Johns Hopkins Univ. Vol, iV.

1896. Browne, E. T« Brii-ish Hydroids and ..edusa?^. Proc.
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1898. Browne, E. T. Keeping ...edusae alive. Journ. ;;ar.

Biol. Assn. V.
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1879. Cianiician, J. Uber die feineren Bau und die Ent-
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1885. Glaus, C. Organisation and Sntwickelung der iiedusen.

1897, Dorflein, F. Die Eibildung bei Tubularia. Zeitschr.

85

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1G97. Gr^rberp, G. i:eitrar;p ^ur Ke- ntnis der Gattunp

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1G92. Hftcker, V. Die Fcrschurr des Fis vcr Aecucria

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86

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07
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1857, i'cCrady, J. Gynr-opthalrata of Charlestor Harbor.

Elliott Sor. Yd Hist.
1886. i'etschnikoff , F. Frbryclopische Studien an Vedusen, 'Vies

1901. Morpenstern, P. Fntvvir/elurr vcr Ccrdyl^rhcra lacus-
tris, Zritschr. Viss. Zrcl. Vol, 70,

{•8
lCr3. ^'urb^ch, I. Zur Krtv,'lrl;plunr der Y.cszelcrgc.^e br? drr

Hydrcicep. Zcrl. AP7Pirrr, XII.
190;^. Pauly, F. UritPmirhunper ttber den Ban 'iPd die Lebe.ps-

v.-eise der Ccrdyln-hcra larustris. Zeitrchr. fUr } aturv;

3d. 3?.
190!?, Perkins, H. F, The Eevelcr^ent cf Gcricnera furbachii,

Acrd. I at. Sci cf FhiladeTrhia.
1871. Schnlze, F. F. Uber den Ban iind die Frtv.icl-elunF vcn

Ccrdvlrrh(i;ra larur-tris. Leirzin.
18f:9. Sir.allv.'crd, ; . lerraria tiarella. Arerica'- latiirali ft ,

ICfS. \'eisrar , A, Die Fntstehnnf: dfr Srxual^ellen bei de^-

Hydrrrediiser . Jera.
If 84. Vilprn, F. E. The Eevelcnre^t cf Eenilla. Fhilcs.

Trrns. CLXXIV.

1900

*e*=^. ilscn, E. B. The Cell. Second Editior. Her York.

1902. V/ulfert, J. Die ETr.brycnalertvdc' e "iinr vor Gcnr-
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89

VITA.
Saruel ?ittenhoiisp var brrr at Fryersford, Perrsyl-
varia or love-ber second 1873. He receiver" his early
ediicatvo- in the District Public Schcols. Later he attended
the "v.ashirrton Hall Collef;iatP Inr.titutr a'~d Ursirus Acader^y,
In the fall of 1697 he ertere',' Ursirus Collef^ej and received
the degree of Bachelor of Arts i- 13"1. In the auturn of
the sare year he entered the Joh-'S HorVins University as a
graduate student; his subjects being Zoology, Physiology
a-d Botany,

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