A monograph of the gymnoblastic or tubularian hydroids

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Alex. Agassiz.

ICibninj of ibc Uluseum

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COMPARATIVE ZOOLOGY,

AT HARVARD COUEGB, CAMBRIDGE, MASS.

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JFtiunSfti bu priViatt substviption, in 1S61.

Deposited by ALEX. AGASSIZ.

No. ^f/y.

THE

RAY SOCIETY.

INSTITUTED MDCCCXLIV.

^7

'rhifs Volume is issued to the Sn/jucribcrs to the Ray Society /is/- the Year 1870.

LONDON

JIDCCCLXSII.

A MOIS ^GRAPH

GYMNOBLASTIC OR TUBULARIAN

HYDROIDS.

GEORGE JAMES ALLMAN, M.D.

DUBLIN AND OXON.,

FELLOW OF THE UOYAL COLLEGE OF SUBGEONS IX IRELAND, F.R.S., F.R.S.E., JI.H.T.A., F.L.S., C.M.Z.S.

EMERITUS REGIUS PROFESSOR OF NATURAL HISTORY IN THE ISIVERSITY

OF EDINBURGH.

TCS^eLUSION OP PAET I,

AND

PART II, CONTAINING DESCRIPTIONS OF THE GENERA AND
SPECIES OP THE GYMNOBLASTEA.

LONDON :

PUBLISHED FOR THE BAY SOCIETY BY

ROBERT HARDWICKE, 192, PICCADILLY.

MBCCCLXXII.

In/A] .

MCZ LIBRARY
HARVARD UNIVERSITY
CAMBRIDGE. MA USA

I'RINTED BY J. E. ADLAHD,
BARTHOLOMEW CT.OSE.

PLATE I.

Cl-AVA SQUAMATA.

Pig.

1. A male colony magnified. Tlie hydrantlis are seen, some fiiU^' extended, others in various

states of contraction.

2. The same, natural size, attached to a piece of Funis nodosus.
;j. A cluster of female gonophorcs.

4. A portion of the h3drantii -walls, after having undergone natural histolitic decom|josition,
very much magnified. The ectoderm is seen to the left, resolved into minute cell-like
elements, limited externally by a delicate structureless pellicle, and separated from the
endoderm by a layer of fibrillated (muscular) tissue. The endoderm is breaking up
into large spherical cells.

5. A male gonophore. The spadix is surrounded by the spermatic mass.

0. A female gonophore. A single ovum, with its germinal vesicle and germinal spot, lies on one
side of the spadix, which it has pushed out of the axis of the gonophore.

7 — 11. Development of the embryo.

7. The embryo still confined within the walls of the gonophore, from which it is ready to escape

into the surrounding water.

8. Embryos liberated as ciliated planulae from the gonophores. They are drawn in various

positions which they are in the habit of assuming, and may be seen either fully extended
or more or less bent uj)on themselves.

9. The planula, after it has lost its cilia and has become contracted longitudinally preparatory

to fixing itself.

10. The planula after it has become fixed and has developed a single verticil of tentacles.

11. The 3'oung C7«z'fl still further developed. A second verticil of tentacles has been emitted

at the proximal side of that first formed, the tentacles of the second verticil alternating
with those of the first ; a stolon has begun to be emitted from the base.

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PLATE II.

ClAVA MCLTICORNIS, ClAVA DIFt'USA, TuBICLAVA FRUTIC'OSA, TUBICLAVA LUCERNA.

Fig.

1. Clava multicornis, magnified.

2. The same, natural size.

3. Clava diffusa, magnified.

4. The same, natural size.

5. Tubichwa fruticosa, magnified.

6. The same, natural size.

7. Tubiclava lucerna, magnified. '.
S. The same, natural size.

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PLATE III.

CORDTLOPHORA LACUSTRIS.
FlO.

1 . Portion of a female colony, magnified ; a, very young gonopliore ; i, gonophore more advanced,

containing ova, which are embraced by the branches of a ramified spadix, and have their
germinal vesicles distinct; c, gonophore still further advanced; the ramifications of the
spadix have disappeared, and the segmentation of the vitelius has been completed in the
ova ; d, further stage of development, in which the ova have become planulae, and are
ready to escape from the gonophore ; e, the gonophore has become ruptured at the
summit, and the ciliated planulae are escaping into the surrounding water.

2. A colony of CordyJopliora lacustris, of the natural size, attached to the under surface of a

piece of floating tiniijer.

3. A male gonophore, the spermatic mass embraced by the ramifications of the spadix.

4. The distal portion of a male gonophore still more magnified : a, external chitinous in-

vestment, showing layers of deposition; 3, ectotheca ; c, endotheca; d, ramified spadix

embracing the spermatic mass.
.5. Planula much magnified, in two different states of contraction. Its interior is occupied by a

large cavity, and an ectoderm and endoderm are distinctly visible in its walls.
G. The planula after it has lost its cilia and has become fixed.

7. Further stage of development, in which the distinction between stem and hydranth has

become apparent, and a verticil of four tentacles has begun to be developed from the
hydranth, while the stem has excreted a delicate chitinous perisarc.

8. The young Cordylophorn still further developed ; the tentacles are still in a single verticil, but

have increased in length, and the hypostome has become prominent.

9. Mature s|)ermatozoa ; in the group to the left the heads are still enclosed in the gene-

rating cell.

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PLATE IV.

CORYNE PUSILI.A, CoRYNE VAGINATA.
FlO.

1. Portion of a female colony of Coryne pusUla, magnified. .

2. A colony of Coryne pusilla, natural size, attached to a piece of Fiicus serralii^.

3. A tentacle of Cori/ne pusilla, very mucli magnified, showing its chambered endode-rm and its

capitulum loaded with thread-cells.

4. A thread-cell from the capitulum before the emission of its contents, and with the superficial

portion of the ectoderm in which it is imbedded carrying a palpocil.

5. A thread-cell from the capitulum after the emission of its contents.

6. Mature ovum of Coryne pusilla, as it appears just after liberation by the natural rupture of the

gonophore. In this stage the germinal vesicle becomes visible under compression.

7. Planula of Coryne pusilla ; the cilia are very long. A peculiar striated area is visible towards

one end.

8. A portion of a female colony of Coryne vayinata. At the left a hydranth-bud is seen,

entirely enveloped in a delicate sac-like extension of the perisarc.

9. A colony of Coryne vayinata, natural size, attached to a piece of Cysfoseira.

I' I IV.

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PLATE V.

Syncoryne eximia.

Fig.

1. A portion of a colony magnified, the hydranth to the left, loaded with planoblasts.

2. A colony, natural size.

3. A planoblast shortly after liberation, very much magnified ; and, as it appears, with its tenta-

cles extended when floating passively in the water ,

4. Terminal portion of a marginal tentacle of the planoblast, showing its continuous axial tube,

and its ectodermal spherules loaded with thread-cells.

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PLATE VI.

Syncoryne pdlchella, Syncoryne frutescens.

Fig.

1. Syncoryne puJchena, magnified.

2. The same, natural size.

3. A planoblast of Syncoryne jndchella, shortly after liberation, as it appears while floating

passively in the water.

4. Syncoryne frutescens, magnified.

5. The same, natural size.

G. Planoblast of Syncoryne frutescens, shortly after liberation.

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PLATE VII.

Gemellaria implexa.

Fig.

1. A portion of a colon \', magnified.

2. A colony, natural size, attached to a piece of rock.

3. A planoblast sliortly after liberation, as it appears while floating passively in the water, very

much magnified. The tentacular appendages are seen with their peduncles in various
states of extension.

4. A marginal tentacle of the planoblast still more enlarged, and with the appendages entirely

retracted.

5. Longitudinal section of a portion of the hydranth showing histological structure : a, ectoderm

with imbedded thread-cells ; b, muscular layer ; c, external large-celled layer of
endoderni; d, internal or glandular layer of endoderra immediately surrounding the
somatic cavity.

6. One of the clavate sacs filled with thread-cells from the umbrella-margin of tiie

planoblast.

7. A thread-cell from the capitulum of a tentacle previous to evolution.

8. The same after evolution.

y. One of the large thread-cells from the ectoderm of the hydranth previous to evolution.
1 0. The same after evolution.

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PLATE VIII.

DiCORTNE CONFEKTA.

Fig.

1. Portion of a colony enlarged. The sporosacs are borne upon blastostj'les, which spring, some

from the hydrocaulas, and some from the hydrorhiza.

2. A colony of the natural size, spreading over a shell of Biiccinuni nndatum.

3. The female locomotive ciliated sporosac, shortly after liberation from its ectotheca, as it

appears vi'hen swimming. It is viewed at right angles to the plane of its two
tentacles.

4. The same viewed in the plane of the tentacles.

5. The male sporosac still enclosed within its ectotheca.

6. The same after liberation from the ectotheca, as it appears when swimming.

7. Longitudinal section of a female sporosac made at right angles to the plane of the tentacles,

and viewed under slight compression.

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PLATE IX.

BOUGAINVILLIA FRUTICOSA, BoUGAINVILLIA RAMOSA, BoUGAINVILLIA BrITANNICA.

Fig.

1. Bougainvillia fndicosa, magnified.

2. The same, natural size, attached to the under surface of a piece of floating timber.

3. A planoblast of the same, just after liberation, and in the act of swiuiming away from its

trophosome.

4. The planoblast floating passively in the water.

5. BougainvUUa ramosa, magnified.

6. A colony of BoiigainvilUa ramosa, natural size.

7. A planoblast of Bougainvillia ramosa, shortly after liberation, as it appears while floating

passively in the water.

8. Mature planoblast [BougainviUia Brifatinica), drawn from a specimen captured in the open

sea. This planoblast has not yet been referred with sufficient certainty to its
trophosome.

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PLATE X.

BOUGAINVII.LIA MUSCUS, HeTEROCORDYLK CoNYBEAREI.

Fig."

1. Bougainvillia mnscm, magnified.

2. The same, natural size.

3. Planoblast of the same, shortly after liberation.

4. Heterocordyle Conijbearei, magnified : a, hydranth, in which the tentacles have assumed a

clavate form as the result of contraction; b, young hydranth ; c, blastostyle extended with
its sporosacs; d, the same contracted.

5. A colony of Heterocordyle Conyhearei, natural size, spreading over a Buccinum shell.
C. Female sporosac of same.

7. Male sporosac of same.

I'l. X.

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PLATE XI.

Perigonimus vestitus, Perigonimcs minctus, Perigonimus serpens.

Fig.

1. Perigonimus vestitus, magnified.

2. The same, natural size, extending over the surface of a Buccimim shell.

3. Planoblast of same, shortly after liberation, and in the act of swimming.

4. Perigoniwus mimdus, magnified.

5. The same, natural size, attached to the operculum of Turritella communis.

6. Planoblast of same, shortly after liberation.

7. Perigonimus serpens, magnified.

8. The same, natiu-al size, on a fragment of Plumularia.

9. Planoblast of the same, shortly after liberation, and seen while swimming.

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PLATE XII.

BiMERIA VESTITA, GaRVEIA NUTANS.

Fio.

1. Bimeria vestita, magnified.

2. The same, natural size.

3. An ultimate ramulus of same, carrying a male sporosac, much enlarged, to show the structure

of the sporosac with its ramified spadix.

4. Garveia nutans, magnified.

5. The same, natural size.

6. Distal portion of tentacle of same, much magnified.

7. A female sporosac of same, much magnified : a, ectotheca invested by a delicate chitinous

pellicle ; b, mesotheca ; c, endotheca ; d, rudimental radiating canals in the proximal
portion of the mesotheca.

8. A male sporosac of same.

9. Spermatozoa of same. The mode in which the head of the spermatozoon is occasionally

curved upon itself is here seeu.

10. Planula of same.

1 1 . Yoiuig of same, developed from the planula.

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PLATE XIII.

EUDENDRIUM RAMOSUM.
Figs.

1. A portion of a male colony cut from the end of a primary branch, magnified. Some of the

hydranths are seen to be loaded with bithalamic gonopliores, while they still retain their
tentacles ; in others, the tentacles have disappeared, and the hydranth has become con-
verted into a pseudo-blastostyle.

2. A colony of tlie natm'al size attached to the back of an oyster-shell.

3. A hydranth, with part of its supporting ramulus, from a female colony. The gonophores

are seen springing, some from the body of the hydranth, and some from the distal part
of the ramulus. In some of the younger gonophores the spadix is seen bending round
the ovum, so as to embrace it in its curvature; in the more mature ones the ovum has
undergone segmentation and fills the cavity of the sporosac.

4. Male sporosac more magnified than in fig. 1.
5 — 16. Development of the embryo.

5. Very young female sporosac containing a single ovum, in which the germinal vesicle and

germinal spot are still visible ; the spadix is seen to be pushed to one side by the ovum,

and to be gradually curving round it.
0. Same more advanced ; the spadix has now almost entirely surrounded the ovum.
7. A still older sporosac, in which the fecundated ovum has attained an advanced stage of

segmentation.
S. Isolated segment-spheres more magnified.
9. Germinal vesicle from an earlier stage of the ovum, isolated, and showing the germinal spot

and its contained punctum.

10. The ciliated planula.

11. The planula after it has lost its cilia, previously to becoming fi.xed.

12. The plamda become fixed by a disc-like enlargement of one extremity.

13. Embryo more advanced; the disc of fixation more decidedly differentiated, while a delicate

chitinous perisarc has become excreted over the whole surface of the embryo.

14. The disc has begun to l)e divided into radiating lobes, and the hypostome has become

differentiated.

15. The hydranth is now distinctly differentiated from the hydrocaulus, while the tentacles have

begun to sprout round the hypostome, and within a delicate chitinous sac, which enve-
lopes the whole.

16. The hydranth has attained to nearly its ultimate form, and has burst through the chitinous

sac, which had hitherto confined it, and the tentacles are now free to extend themselves
in the surrounding water.

17. Spermatozoa. A minute corpuscle, like a parietal nucleus, is seen adherent to the head

of each.

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PLATE XTV

EUDENDRIUM CAPILLARE, EuDENURIUM IXSIGNE,' EuDENDRIUM VAGINATUM.

Figs.

1. Eudendriion capillare, male colony, magnitied. The sporosacs are bithalaniic, and the

hydranths which carry them arc all atrophied and converted into pseudo-blastostyles.

2. A colony of Eudendrium cajjiUare, natural size.

3. An atrophied hydranth of Eudendrum capillare, carrying female sporosacs. The spadix

curving round the ovum.

4. A portion of a male colony of Eudendrum hisigne. One of the hydranths loaded with

sporosacs,

5. A colony o^ Eudendrium insigne, natural size.

6. Summit of a hydranth-bearing ramulus, from a female colony of Eudendrium insigne, carrying

sporosacs. The spadix curving round the young ovum.

7. Eudendrium vaginal urn, portion of a colony, magnified. A young hydranth-bud, as yet

destitute of tentacles, is seen to be enclosed in a delicate chitinous capsule, while a sheath-
like extension of the perisarc invests the body of the mature hydranths.

8. Eudendrium vaginatum ; a colony, natural size.

^ Named " humile " in the plate. For the reasons of change of name, see the description of the
species, page 337.

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PLATE XV.

Hydractinia echinata.

Figs.

1. Portion taken from near the margin of a female colony, magnified; a, a, a, hydranths in

various states of contraction ; b, h, b, blastostyles laden with sporosacs ; c, c, c, spiral
zooids.

2. A colony, natural size, spreading over the surface of a buccinum shell inhabited by a

hermit crab.

3. A blastostyle from a male colony, more magnified than fig. 1, laden with sporosacs.

4. Transverse section of one of the chitinous spines from near the base; a, ectoderm investing

the surface of the spine ; b, endoderm occupying its furrows and channels ; b', one of
the tubular cavities of the endoderm with its coloured lining ; c, one of the longitudinal
chitinous ridges of the spine.

5. Transverse section of one of the chitinous spines from near the summit.

6. A female sporosac seen in longitudinal section.

7. Longitudinal section of one of the chitinous spines; a, superficial covering of ectoderm.

b, b, endoderm with its included cavity occupying the superficial furrows of the spine .

c, c, the chitinous walls of the spine showing successive layers of deposition ; d, d, longi-
tudinal chitinous ridges ; e, e, proximal portions of two hydranths developed from the
superficial ccenosarcal investment of the spine.

I't XV.

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Ilvdraciinta cckinata

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PLATE XVI.

PODOCORYNE CARNEA, HyDRACTINIA ECHINATA.

Fig.

1. Portion of a colony of PoJoconjne carnea, magnified; a, a, a, sterile hydrantlis in various

states of contraction ; b, b, proliferous hydrantlis laden with planoljlasts, the planoblasts
in various stages of development.

2. A colony of Podocoryne carnea, natural size, spreading over the surface of a piece of

submerged rock.

3. A planoblast just after its lil)cration from the trophosome floating in the water, and with

its tentacles extended.

4. The same with its tentacles contracted and thrown up round tlie margin of tlie umbrella.

5. Planoblasts in the act of swimming seen at the moment of systole, the umbrella strongly

contracted and assuming a conical form.

6. A free planoblast more magnified, floating in the water, and with its tentacles extended.

7. One of the oral lobes of the manubrium of the planoblast showing its pencil of stalked

thread-cells.

8. Portion of the umbrella-margin of a planoblast ; a, marginal tentacle ; b, a radiating canal ;

e, circular canal; d, ectoderm of margin, where it forms a cushion-like thickening on the
bulbous root of the tentacle; c, ectoderm continued round the extreme margin of the
undu'clla.

9. A [)ortion of the common basis of a young colony, showing its coalescent chitinous tubes.

10. Ilj/dractiuia echinata, vertical section through the common basal expansion extending from

the free towards the attached surface ; some of the coalescent chitinous tubes filled with
ccenosarc, others empty ; «, «, superficial layer of ectoderm extending over the free
surface ; b, cocnosarcal tube lying in one of the superficial chitinous channels ; c, c, walls
of the adnate chitinous tubes ; % proximal extremity of a hydranth, its cavity continuous
with that of one of the ccenosarc tubes of the common basis.

11. Portion taken from the edge of the basal expansion in a colony of ITijdractinia echinata,

where it had been injured and is undergoing reparation ; the chitinous tubes, with their
cocnosarcal contents, are seen extending themselves in the form of a network, the meshes
of which subsequently become obliterated by the coalescence of the chitinous walls.

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PLATE XVII.

Cladonema kadiatum, Stauridium productuai.

Fio.

1. A colony of Cladonema radiatum, magnified. The drawing has been made from the free

variety of this hydroid. (See the description of the species, page 358.)

2. The same, slightly larger than natural size.

3. Cladonema radialum, a free mature planoblast floating in the water.

4. The same fixed by its appendages of attachment, and with its marginal tentacles thrown

back over its umbrella.

5. A marginal tentacle contracted ; the three appendages terminating in spherical capitula near

the base of the tentacle are the appendages of attachment, and do not participate in the
contraction undergone by the rest of the tentacle and its branches. The ocellus, with its
pigment and refracting body, is seen in the enlarged base of the tentacle.

6. Extremity of one of the nodulated branches of a marginal tentacle slightly contracted.

7. Origin of the radiating canals as seen from the summit of the umbrella.

8. Velum showing its great width and its circular and radiating fibrillae.
y. Planoblast at the period of its liberation.

10. Mature planoblast, natural size.

11. Stauridium jjrodtict urn, a colony magnified.
13. The same, natural size.

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PLATE XVIII.

Clavatella prolifera.

Fig.

1. A colony, magnified.

2. The same, uatni-al size.

3. One of the tentacles of the hydranth much magnified.

4. The free ambulatory medusa (planoblast) as seen when it has attached itself by its suctorial

discs.

5. The planoblast viewed from the vertex, showing the radiating and circular canals. «, a

young medusa-bud ; h, a medusa-bud more advanced.

6. The ocellus showing its pigment and refracting body.

7. Extremity of a marginal tentacle of the planoblast showing its two branches, one of which

is provided with a suctorial disc of attachment.

8. Vertical section of planoblast showing ova carried in its summit between ectoderm and

endoderm ; 'a, mouth ; h, h, marginal tentacles.

9. Young medusa-bud developed from the base of the hydranth.
10. Medusa-bud more advanced, marginal tentacles still simple.

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PLATE XIX.

CORYMORPHA NUTANS.
FlO.

1. The entire hydrosoma, magnified; a, papilliform processes from the stem; h, h, filamentary

appendages emitted from the proximal end.

2. A group, natural size, as it appears when confined in an aquarium, the proximal ends

plunged into the sandy bottom. This may fairly be taken as representing the mode of
existence of Corymorplia nutans in its natural habitat at the bottom of the sea. Some
planoblasts just liberated are seen swimming about.

3. One of the branched peduncles from the gonosome carrying gonophores in various stages of

development, more magnified than fig. 1.

4. A planoblast shortly after liberation ; its tentacle contracted. Much magnified.

5. Mature male planoblast, magnified.
5a. The same, natural size.

6. Transverse section of the stem about the middle of its length ; a, delicate external pellicle ;

h, ectoderm ; c, fibriliated layer, d, peripheral portion of endoderm composed of small
spiierical cells with coloured granular contents, and excavated by longitudinal canals ;
e, axial portion of endoderm composed of large polygonal cells with clear homogeneous
contents.

7. Longitudinal section of hydranth ; a, distal portion of hydranth cavity; b, proximal portion

communicating with « by a narrow axial channel, and receiving the longitudinal canals,
c, of the stem ; d, ectoderm ; e, outer clear-celled portion of endoderm ; /, inner portion
of endoderm lining the hydranth cavity, and composed of cells with coloured granular
contents ; g, base of proximal set of tentacles ; h, base of distal set ; /, peduncles of the
gonophores.

8. Portion of a proximal tentacle of the hydranth seen in longitudinal section.

9. Portion of a distal tentacle of the hydranth seen in longitudinal section.

10. One of the papilliform processes of the stem extended.

11. Same, contracted.

12. Free frustule of Corymorpha nutans contained within its delicate chitinous tube which

adheres to the sides of the jar.

13. The same body after it has become fixed by one end and developed a hydranth from the other.

14. The same, more advanced.

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PLATE XX.

TUBXJLARIA INDIVISA.

Fig.

1. A male colony of Tubularia hnlivisa, natural size; a, young individuals which had attached

themselves to the stems of the adult colony.

2. A hydranth from a male colony, with its pendulous raceme-like clusters of gonophores,

magnified.

3. One of the raceme-like clusters of gonophores from a female colony. The sporosacs, with

their contents, are seen in various stages of development. Close to the root of the
common peduncle the very young sporosac-bucis may be seen in the form of densely
aggregated, sac-like diverticula from the tube of the peduncle. As these approach the
distal end of the peduncle they are seen to become more and more developed ; the gene-
rative plasma surrounding the spadix has become distinct, then this is seen to have
thrown off masses which become developed into actinulaj ; the actinute gradually assume
their complete form, and at the extreme end of the raceme they are seen fully developed,
escaping through an orifice in the summit of the sporosac.

4. An actinula shoi-tly after liberation. It is figured in the attitude assumed when moving

from place to place ; the mouth is turned towards the surface^ over which the actinula is
ujoving, while some of the long tentacles are bent in the same direction, and are
employed as ambulatory organs.

5. The actinula after it has permanently fixed itself It has developed a stem, thrown out

hydrorhizal processes of attachment, and excreted a periderm. The endoderm of the stem
has already become canalliculated as indicated by distinct longitudinal striae.

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PLATE XXI.

TUBULARIA LARYNX.

FlOS.

1. A hydranth from a male colony, with its long simple racemes of gonophores ; magnified.

2. A hydranth from a female colony, with its shorter compound racemes of gonophores ;

magnified.

3. An entire colony, natural size.

4. A portion of the hydrocaulus, showing the interrupted annulation of the perisarc ; slightly

magnified.

5. Summit of stem much magnified, showing the fluted collar-like expansion, a, of the

ectoderm. The perisarc is continued from a point at a little distance below the collar as
a thin filmy and transjjarent tube over the distal portion of the stem.

6. An actinula some days after its liberation, as it is seen floating in the surrounding

water ; magnified. The oral tentacles, which are absent at the period of liberation, have
already become developed.

7. The actinula after it has permanently fixed itself. It has developed a stem which is clothed

with a chitinous perisarc, and has emitted hydrorhizal processes of attachment. The
young stem is excavated into a single cavity instead of being traversed by several longi-
tudinal canals, as in the corresponding stage of Tiibidaria uidivim. Very distinct
currents are visible through the transparent walls of the stem, as indicated ])y the arrows
in the figure.

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PLATE XXir.

TUBULARIA ATTENUATA, TURUI.ARIA HUMILIS, TUBULARIA BeI.LIS.

Fios.

1 . Tubularitt (itlciiuala, a liytlrantli from a male colony, with its short erect clusters of gono-

phoros ; magnified.

2. A colony of Tiihidarki ntleniiata, natural size.

3. Tiihnlaria liuwilis, a hydranth from a male colony, with its short erect clusters of gonopliores;

magnified.

4. A colony of TuhuJaria /nin/ilis, natural size.

0. Tubnlaria Bellix, a hydranth from a female colony, with its erect clusters of gonopliores, in
some of which the actinuhne may be seen already developed ; magnified.

n. A colony of Tnhularin Jicllis, natural size.

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PLATE XXTIT.

TUBULARIA INDIVISA AND TuBULARIA LaRYNX. AnATOMY AND DEVELOPMENT.
Fig.

1. 2\i./mlaria indivisa, \ii\-\.\cvi\ section through the body of the hydrniith ; «, endodenn liiiiiio-

the distal portion of tlic hydranth cavity ; h, endoderin lining the pro.\inial portion ; c,
pendulous lobes of endoderm separating the distal from the proximal portion of the
hydranth-cavity. (See page 124.)

2. Pendulous endodcrmal lobes in hydranth-cavity of Tuhularia indivim ; profde view.

3. A single lobe more magnified.

4. Tuhidaria indivisa, one of the tentacles of the distal circlet, focalised in a longitudinal plane

passing through the axis, and showing the ectoderm, endoderm, and intervening fibril-
lated layer. (See page 200.)

5. Tiihihtria indivisa ; portion of one of the proximal zone of tentacles, showing the fihrillse of

the muscular layer. In the ectoderm some thread cells are seen witli the filament
exserted.
0. Some of the fibrilltC of the muscular layer isolated and mngnitied about 200 diameters.
(See p. 206.)

7. 7'«^«/ffn'« zV«/zV/««, transverse section of the stem; «, perisarc showing numerous successive

layers of thickening ; b, ectoderai ; c, peripheral layer of endoderm composed of small
spherical cells with coloured granular contents, and excavated by the longitudinal ciliated
canals ; d, central portion of the ectoderm composed of large cells with clear, colourless
contents, and forming a solid, pith-like axis. (See p. 206.)

8. Tuhularia indivisa, male gonophore; a, ectotheca ; ^, mesotlieca ; c, radiating canal; d,

circular canal ; e, endotheca ; /, spermatic mass ; immediately over the circular canal is
seen the apical orifice of the gonophore. (See page 207.)

9. Free spermatozoa of Tuhularia indivisa.

10. Tuhularia indivisa, transverse section through spadix, showing its ciliated cavity and its

proper tissue surrounded by the spermatic plasma. (See page 207.)
11 — 10. Development of actinula in Tuhularia indivisa. (See page 90.)

11. Female gonophore; r/, ectotheca ; h, mesotheca ; c, radiating canal; d, apical orifice sur-

rounded by circular canal ; /, generative plasma enveloping the spadix ; y, mass detached
from generative plasma, and about to become developed into an actinula. The endotheca
has already disappeared.

12. Cells composing the mass detached from the generative plasma {(/ in fig. 11).

13. The actinula in a very early stage. It is in the form of a concavo-convex disc, which

embraces the spadix and residual plasma. Its interior is hollowed out into a cavity.

14. An ectoderm and endoderm has become differentiated, and the margin presents a shallow

lobing, the commencement of tentacles.

15. The tentacles have become distinct, having increased in length, and the embryo now presents

the form of a star.

16. The actinula is fully formed and ready to escape from the gonophore; a circle of short

tentacles, a, has become develojied round the mouth.

17. Thread-cells from the hydranth of Tuhularia indivisa; a, ordinary form of thread-cell before

evolution ; h, the same after evolution ; c, minute bean-shaped thread-cells.

IS. Cells from the lining of the hydranth cavity in Tuhularia larynx. Some of these cells
contain within them clear secondary cells ; in others the secondary cells contain a brood of
still younger cells, or are filled with a coloured granular matter. Some of the secondary
cells with their granular contents are seen in the figure to have been liberated by the
rupture of the mother-cells. (See ])age 134.)

19 — 24. Development of actinula in Tuhularia larynx. (See page 91.)

19. Very young female gonophore; a, ectotheca; h, endotheca; /, generative plasma.

20. Cells composing the generative plasma in fig. 19 treated with acetic acid, and magnified

about 250 diameters.

21. Gonophore at a more advanced stage than fig. 19; a, ectotheca; d, commencement of apical

processes ; h, endotheca ; /, generative plasma.

22. Cells composing the generative plasma in fig. 21 treated with acetic acid.

23. Gonophore still more advanced; the apical processes have become larger, the endotheca has

disappeared, and the generative plasma has thrown off a mass which is about to become
developed into an actinula ; /, residual plasma enveloping the spadix ; g, mass which had
been detached from the ])lasma.

24. Gonophore containing a fully developed actinula in the act of liberation ; /, residual plasma

enveloping the spadix ; y, a mass which had been detached from the plasma, lying free in
the cavity of the gonophore ; li, h, completely formed actinula escaping through the
orifice between the apical processes of the gonophore.

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