-' V UC-NRLF III! II I I II J\ C 2 773 323 PtBPH ii jri A. >^WWVWM n 81 ^- ^^r if ' A -V ^ ' '^ '^x vx v_ y \jx ' '^ ; aioiocr LIBRARY w- A NEW FAMILY OF HYDROIDEA. BY W. BALDWIN SPENCER, MA. REPRINTED FROM THK TRANSACTIONS OF TIIK UOYAI. Sorn.iv or VICTORIA FOK Is'.iu. * BIOLOGY LIBRARY G i>irially towards the central part, in a direction generally parallel to the length of the branch. E. spaces or grooves, immediately beneath the thin external layer. Hy. hydrothecae. P. thin external layer of perisarc. P'. the continuation of P. to form an operculuin at the mouth of the hydrothecae. P". the iieinatophores. x35. Figure 8. A transverse section of a small branch, to show the tubes of which it is composed. The tubes vary in size, and open into one another. The outer ones are incomplete externally, forming grooves, the lips of which are usually touched by the thin external layer of perisarc. Two hydrothecae are cut through. The perisarc is thicker towards the outer than in the inner part of the branch. Letters as in Fig. 7, x 70. Figure 9. A small portion of the external part of a branch very much enlarged to show the roughly concentric layers of which the perisarc is formed. Letters as in Fig. 7. Figure 10. Small portion of a ccenosarcal tube with the perisarc walls from the interior of a branch. Ect. the ectoderm in which the outline of the cells cannot be clearly distinguished, and which varies in thickness in various parts coming in contact, in certain places, with the perisarc walls. End. the unilaminar endoderni, the cells of which are larger than those of the ectoderm, x. globular structures of unknown significance containing darkly staining parts which lie apparently within the cavity of the tube. Drawn under Zeiss F. oc. 2. Plates 21, 22, 23 refer to Plumularia procumbens. PLATE 21. Figure 17. Restoration of the soft parts only of Plumularia procumbens. The polysiphonic stem is shown in section with the transverse connections between the various tubes which compose it. Down the centre runs the main tube from which arise all the lateral branches pinnae and hydrocladia which are in connection with a varying number of the surrounding tubes. The most external ones give off numerous machopolypes, and on the pinnae are shown the groups of polypes, each consisting of one gastrozooid and three machopolypes. One blastostyle is shown with a gonophore, arising from the angle between a pinnule and the main stem of the pinna, x 30. Figure 18. Longitudinal section of a male gonangium with its contained blastostyle and gonophore. In the centre of the gonophore lies the mauubrium. Bl. 140 A NEW FAMILY OF HYDROIDEA. blastostyle. D. swollen distal, end of blastostyle. Sp. sperm. G. walls of gonotheca. Figure 19. Transverse section of a male gonangium and gonophore. On the left side between the gonophore and the wall are seen traces of the much compressed blastostyle. End. endoderm of manubrium. Ect. ectoderm outside sperm cells (sp.) PLATE 22. Figure 20. Portion of a colony of Plumularia procumbent showing the poly- siphonic stem and the pinnae arising irregularly from this, x \\. Figure 21. Much enlarged portion of a pinnule or hydrocladium to show the alternate longer and shorter joints. The latter bears no hydrotheca or nematophores ; the former bears a hydrotheca with the nematophores at the level of the mouth of the former, and one in the median line below. The thickenings in the walls of the pinnule are shown in their positions and the two nematophores in the axil between the pinnule and the main stem of the pinna, and at A, the conical structure opening to the exterior. N 1 . upper pair of nematophores. N 2 . lower median nematophores. N 3 . nematophores in the axil of the pinnule and pinna stem. A. conical process in the axil leading from the interior of the pinna to the exterior. Figure 22. Much enlarged view of a nematophore seen in optical section, and showing the two chambers. Figure 23. Much enlarged view of a male gonangium. Figure 24. Semi-diagrammatic drawing of a longitudinal section of the poly- siphonic stem of the same to show the relationship of the hard and soft parts and the distinctness of the central tube with its walls slightly yellower than those of the surrounding tubes. C. central tube. H. central stem of pinna. H'. hydrocladia. L. lateral tubes. N. nematophores. T. transverse connections uniting the various tubes, x 30. PLATE 23. Figure 25. Much enlarged view of the termination of a polysiphonic stem, showing the numerous nematophores on the stem and the pinnae &c., arising irregularly. The basal parts of the pinnae are strengthened by the formation of a thick perisarc wall continuous with that of the tubes forming the stem, x 20. Figure 26. A highly magnified portion of a pinna. Figures 27 and 28. Transverse sections of the polysiphonic stem to show the component tubes skeleton only with the large central one, from which in figure 28 a pinna is arising. The external tubes are studded with nematophores. T*ans.R. Victoria Plate I! CLATHROZOON WILSON Q /g '; - i / . f V* ; ,' '*.';. ' 4 - 3 * ' \\imm jfe^ Ww^i^&Z%& \ ' I* i' i It tfe r ^S^f- ,&/* Spencer del , /' rono. Plat F>g 16. Fig 14. Fig 13 Trans, R.S. V/c/orto. P/ate 20. P..- E fig let- WJ3 Sfsncer deL C.TneddiC' Luh. Melb. Fy 84 V XT RS V/cfor/e ftefe 23, ids Flak MM ON THE STRUCTURE OF CEKATELLA FUSCA (GRAY). By W. BALDWIN SPENCER, M.A., Professor of Biology in the University of KIcllii'in n, . *{iri;ivni. iiin.M -nil. THAN- ... ilu: Kov.M, Som/iv and Fig. 7 ; PI. XVIII.,- Fig. 1. 14 ON THE STRUCTURE OF CERATELLA FUSCA (GRAY). continuous with the ectoderm of both the hydroid zooids and the gonophores, and has in many respects a close resemblance to the superficial layer of ectoderm as described and figured by Professor Moseley in Millepora.* In the latter the exact relationship of the superficial ectoderm to the zooids could not be ascertained but in Ceratella where the latter are not retracted into spaces within the skeleton its direct connection with the ectoderm of the zooid can easily be seen in sections. Figure 3 represents a small portion of the layer as seen under a high power. The outlines of cells cannot be definitely distinguished in the specimen in question though a somewhat light space with a fairly distinct outline surrounds the thread cells. The inner ends of the cells are in contact with the ectoderm of the tube beneath and the layer thins out just where it passes over the projecting point of a portion of the skeleton. In younger branches (Fig. 14) the cells of the layer are much more definite in form and outline being each cubical with a distinct nucleus whilst comparatively very few thread-cells are present. This superficial layer is only known to exist in the Hydrocorallinse, the Hydractiniidae and, now, in the Ceratelladas. In the last mentioned the soft parts of only Ceratella fusca are known as yet but the skeleton of Dehitella is so closely similar to that of the former that we may with much probability infer that a close agreement exists in the nature of their soft parts. The coenosarc tubes form a richly branching network of tubes occupying all the spaces in the chitinous meshwork which forms the skeleton. In Figures 9 and 10 this is represented diagrammatically by the grey colour the former being a longitudinal and the latter a transverse section of a branch. Throughout the whole system the endoderm is never more than one cell thick whilst the ectoderm is very irregular. Very often the endoderm cannot be recognised or else it forms an indistinct layer which stains more darkly than the ectoderm and contains no space, a result probably due to the action of reagents. At other times (Figs. 3, 11, 12, and 14) a distinct tubular space can be distinguished. The number of tubes varies naturally according to the size of the branch. Figure 13 represents a longitudinal section through a portion of a small branch with a smaller offshoot which formed part of a specimen brought by Mr. Whitelegge from Lord Howe Island. The general appearance of a part of the same specimen viewed as a solid object is represented in Figure 4. This particular specimen has the branches much finer than those of the others and the skeleton and ccenosarc tubes somewhat more regular in arrangement, whilst the hydrophores are not very strongly developed. Up the small offshoot pass the main skeletal ribs united by cross bars which are thin and almost web-like and up the centre runs a single coenosarc tube (B) which is connected with at least three of those in the larger branch. This tube consists of an internal layer of endoderm (Fig. 13 a, end.) and * On the Structure of a Species of Millepora occurring at Tahiti, Society Islands. Phil. Trans. B.S. London, 1870, Vol. CLXVII., p. 117. ON THE STRUCTURE OF CEHATELLA FU8CA (GRAY). 15 an irregnkur external layer of ectoderm (ect.) the former being continuous with that of the xooids. The whole is covered by a uuilaminar ectoderm (E). A few thread cells are present. Up the layer branch the tubes run more regularly than usual and three or four may be traced for a considerable distance running parallel to its length but giving off lateral branches. In sections both transverse and longitudinal of Ceratella these connecting bars or webs crossed by ccenosarc tubes form a very characteristic feature (Figs. 11 and 13. C). As stated above there is a strongly-marked difference between the endoderm and ectoderm. The former (Fig. 3) is regular and takes stain somewhat more readily than the latter, which is often very irregular and several cells thick, though most often the outlines of cells cannot be recognised, and a structure resembling a syncytium is formed. In the latter are found (1) nuclei, (2) thread cells, (3) bodies surrounded by a clear space and staining evenly and deeply (Fig. 3A). The thread cells are apparently confined to the ectoderm, though of this I cannot feel absolutely sure, and are found in great abundance in the inner parts of the branch whence they must migrate to the surface if they are to be of service to the colony. It is a somewhat curious fact that they are as a rule present in far greater numbers iu the ectoderm of the cosnosarc tubes than in the most external layer. Figure 3 represents a small portion of the latter on a part of a colony where the gonophores were numerous and here thread cells were present in greater numbers than elsewhere. Of the nature of the third-named structures it is difficult to be certain but it is probable that they are ectoderm cells in which thread cells are being formed. There is at all events a curious agreement in appearance between them and the structures which Professor Moseley has described as developing thread cells in Millepora.* He says " the thread cell appears to be developed out of the nucleus of the ectodermal cell, the ectodermal cell becoming much enlarged and forming a wide chamber, in which the process of development takes place. The ovoid nucleus becomes enlarged together with the cell, but not at all in the same proportion the cell always appearing as a wide cavity around it. The nucleus as it enlarges has a rounded nucleolus developed at one end of it." The nucleolus has large granules developed within it, whilst the nucleus becomes finely granular. In the next stage one large coil of the thread appears in the nucleus." The earlier stage seen in Millepora when the nucleus with nucleolus at one end of it lies in the cell which forms a clear cavity around it, corresponds exactly to that represented in figure 3A.c. in the case of Ceratella. Though a complete series of stages could not be obtained still those drawn in figure 3A. will serve to show that in all probability Ceratella resembles Millepora closely in the formation of thread cells. In figure 3A.rt. the cell is small and the nucleus but little larger than that of an * Loc. cit., p. 129. 16 ON THE STRUCTURE OF CERATELLA FUSCA (GRAY). ordinary ectoderm cell though stained very deeply and having a homogeneous appearance ; in b. the cell has increased in size, the nucleus is much larger, and has a clear space all around it between it and the cell wall ; this is clearly marked in c. and d. where, in the former, a nucleolus is present and in the latter two darker thread- like lines possibly indications of the commencing formation of the thread ; in c. what is evidently a very young thread cell is seen it is somewhat darkly stained without a definite thick wall such as is seen clearly in later stages, and down the centre is a lighter line corresponding to the thicker attached part of the thread. It has also the shape of the thread cell but there is no trace of the clear space present in earlier stages, a certain amount of stained protoplasm being attached to it. In/. and#. two later stages are shown in which the thick cell wall is present and the coiled thread can be clearly seen. These thread cells evidently resemble closely in structure the three-barbed ones described by Professor Moseley in Millepora. The only other point to notice in regard to the coonosarc is the structure of the finer growing branches which are somewhat flattened out. A longitudinal section of one of these is represented in figure 14. Up the centre runs a coenosarc tube with a large cavity and clearly-marked endoderm the ectoderm being as usual irregular. From this central tube short branches are given off (D) which run outwards towards the external layer with which, as at the point x, they may come into direct contact. At this point the cells of the two layers are well marked, and in all probability this shows us the earliest stage in the formation of a zooid. It has already been noted that the ectoderm of the latter is in direct connection not with that of the coBiiosarc tubes but with the common external layer and this method of formation would explain this otherwise somewhat curious fact. The endodermal process grows out into a bud the early stage of a zooid carrying with it the external ectoderm layer which thus, as further growth takes place, naturally gives rise to that of the zooid itself. At the same time the ccenosarc tube branches as the stem increases in size and thus the zooid, if the branching be near the base of the latter, will become connected with two or more tubes. AFFINITIES OF THE CERATELLADTE. When Dr. Gray first described these forms there were only two specimens available neither of which possessed the soft parts. The hard parts whilst agreeing in important points differed from each other sufficiently to be regarded by him as species of two distinct genera Ceratella and Dehitella. Mr. Carter, with more material at his disposal, recognised the fact that they were hydroids and owing to similarities in their skeleton and that of Hydractinia placed them in the family Hydractiniidae, thus abandoning Dr. Gray's family Ceratelladao which had been created under the assumption that the two forms were allied to the sponges. ON THE STRUCTURE OF CERATELLA FFSCA (GRAY). 17 I'ndoubtedly in many rospocts Ceratella and Dehitella call to mind the Hydraetiniidir, but it is doubtful if even our knowledge were confined to that of the structure of the hard parts whether Mr. Carter's classification could be upheld. The one point of resemblance and at first sight it is the most striking feature is that the skeleton of both consists of a very irregular branching chitinous network. In the Ilydractiniido) however this has the form of an encrusting network with at most very feebly developed branches arising from it ; these may more correctly be described as spines and they do not appear to carry any zooids. In the CeratelladiO the whole colony consists of a much-branching structure arising from a compiratively small encrusting root-portion which may itself be made up of branches more or less entwined. In addition to this all the branches bear hydrophores or special developments of the network to support the hydroid zooids. These are never present in the Hydractiniidne but always in the Ceratelladze. Now that the soft parts are known there can be no doubt about separating the two families. The hydroid zooids are quite different those of Ceratella being provided as arc those of Coryne with scattered capitate tentacles whilst there is no trace of protective zooids such as are present in Hydractinia and Podocoryne. In addition to this the gonophores arise directly from the coenosarc and not from modified zooids. The most important points of agreement lie in (1) the existence in Hydractinia and Ceratella of a common external layer of coanosarc which covers over the whole skeleton mass whether this be encrusting or branching in nature ; (2) the presence in both of a network of coenosarc tubes forming the hydrophyton. It may however be noted that in both these points we find a similar agreement to exist between Ceratella and, for example, Millepora amongst the Hydrocoralliuae as between the first named and Hydractinia. The presence of this external layer which, in the Hydrocorallinffl and Ceratella at all events, consists simply of a layer of ectosarc is very difficult to explain. Professor Moseley* lias represented it in Millepora as if it formed the outer layer of the surface cconosarc tubes though even in this case it passes over all the parts (occupied by the calcareous skeleton) which on the surface lie between the tubes, and is very different in appearance and in the relative size of its cells from the ectoderm which elsewhere forms the outer wall of the tubes. In Ceratella it is perfectly independent of the tubes all of which have their own ectoderm covering though at the surface this comes in direct contact with the outer layer. I am not aware of any determination in Hydractinia of the exact relationship of this outer layer though very probably it will be found to agree with that of Ceratella. It is not apparently connected in any special way with the formation of the chitinous network as this lies deep within the structure of the branch, and the only * Loc. cit., PI. 3., Figs. 10 and Hi. 18 ON THE STRUCTURE OF CERATELLA FUSCA (GRAY). purpose which it can apparently serve is that of a covering layer which prevents foreign objects from passing in between the meshes of the network and interfering with the general welfare of the colony. It is strange however to note, if this be its function, that most usually the internal ccenosarc contain a far greater number of thread cells than this external layer does in Ceratella. In Millepora Professor Moseley was unable to determine its exact relationship to the zooids but in Ceratella by its means all the ectodermal structures lying on the external surface are brought into direct continuation with one another. It may be noted in passing that though in the genus Clathrozoon* the branches of the colony are formed of a somewhat similar network of soft parts there is nothing present resembling this external layer the whole branch being in this instance covered with a thin protective perisarc. Taking both the hard and soft parts we find the following points of agreement to exist between the Hydractiniidae on the one hand and the Ceratelladae on the other though it must be borne in mind that we only know as yet the structure of the soft parts in one member of the latter family. (1.) The skeleton has the form of a branching chitinous network. (2.) The hydrophyton consists of a network of freely branching and anastomosing ccenosarcal tubes. (3.) The zooids arise directly from this network and no true hydrothecae or gonothecas are formed. (4.) A common external layer is present enclosing the whole colony. The two differ from one another in the following points : (1.) Hydractiniiclae form encrusting masses with at most spinulose branches arising from the surface which do not bear zooids. The Ceratelladae always form freely branching masses either erect or procumbent : the basal part which serves to attach the colony being alone of an encrusting nature whilst even this has the form of intertwined branches. (2.) The Ceratelladae always possess hydrophores or special developments of the skeleton which serve as a support for the basis of the hydroid- zooids and nothing similar to which is found in the Hydractiniidae. (3.) The hydroid zooids Ceratelladae possess scattered capitate tentacles those of the Hydractiniidae being filiform and arranged in a single circle beneath the mouth. * Tiaus. B.S., Victoria, 1890, p. 121. PI. 18, Fig. 3; PI. 19, Fig. 12. ON THE STRUCTURE OF CEUATELLA FUSCA (GRAY). 19 (4.) Tlic gonophores of the Ceratelladae arise directly from the ccenosarc and are not developed on special zooids as in the case of the Hydractiniidte. Whilst the points of agreement detailed above serve to show a general resemblance between the members of the two groups those of difference are of sufliricnt importance to justify their separation into two distinct families. As stated previously Dr. Gray's name Ceratelladre will be retained and the following gives the characters of the family (modified from Dr. Gray's and Messrs. Carter and Bale's descriptions) and the list and characters of the genera and species yet kno\\n. Family Ccratclladcc (Gray, Proc. Zool. Soc., 1868, p. 575). Forming branching colonies. Skeleton in the form of a chitinous network with slight bracket-like or tubular projections (hydrophores) serving as a support for the bases of the gastrozooids. Hydrophyton a network of branching anastomosing tubes the whole enclosed by a common ectoderm layer. Gastrozooids naked. Gonophores medusoid : fixed and arising directing from the hydrophyton. Genus. Dehitella. (Gray.) Colony dichotomously branched, expanded growing in a large tuft from a broad creeping base. Stem cylindrical, smooth ; branches tapering and cylindrical. Hydrophores slightly tubular and on the smaller branches divergent nearly at right angles from the stem. (1.) Dehitella atrornbcns. (Gray.) The description of the species is the same as that of the genus. It is known at present simply from that given by Dr. Gray* who states that the genus " is distinguishable from Ceratella bythe greater thickness and cylindrical form of the stem, by the more tufted and irregular manner of growth and by the tufts of spicules (oscules or cells) being more abundant and equally dispersed on all sides of the branches and branchlets." The " oscules or cells " of Dr. Gray must be the structures which, following Mr. Bale, have been described above as " hydrophores." Locality. Delagoa Bay, Africa. * Proc. Zool. Soc. 18U8, p. 679. Fig. 1. 20 ON THE STRUCTURE OF CERATELLA FUSCA (GRAY). Genus. Ceratella. (Gray.) Colony irregularly branching ; more or less expanded in one plane ; growing from a creeping base. Main stem flattened, branches rounded and beset with bracket-like hydrophores. (2.) Ceratella fnscn. (Gray.) Colony branching and fan-shaped ; expanded in the one plane ; erect. Skeleton consisting of a light or dark-brown chitinous network ; the main stem broad and flattened ; brandies numerous with the bracket-shaped hydrophores nrranged on them in a roughly spiral manner and formed of ribs continuous with the fibres of the stem and united by thin perforated lamina; the ribs projecting at the outer margin. All the spaces within the chitinous network filled by a much branching hydrophyton and the whole enclosed by an external layer of ectoderm. Gastrozooids seated on the hydrophores, erect, with capitate tentacles irregularly scattered (10-14). Gonophores medusoid, fixed. Localities. Coogee, Bondi (N.S.W.), Broughton Island, Flinders Island, Lord Howe Island. (3.) Ceratella procnmbcns. (Carter*). Colony procumbent, thickly branched on the same plane ; the larger stems chiefly on one (the lower) side, hard, flexible, of an ochre-brown colour, tinged here and there with purple. Trunk short, solid, compact, compressed vertically, soon dividing irregularly or subdichotomously into round branches which are confined to the lower surface, ending in branchlets with sub-clavate ends, that appear on the upper or opposite side, not reuniting or anastomosing. Hydrophores consisting of a little semitubular plate, extending outwards and forwards from the side of the stem on the proximal border of an aperture in the latter; scattered thickly over all the branches, but most prominent on the branchlets ; frequently represented by the little hole alone in the stem where the projecting portion lias been worn off; scanty on the lower side of the main stems. Minute structure ; composed of clathrate chitinous fibre throughout, whose meshes are subrectangular ; hydrophore formed of the semitubular scoop-like plate mentioned supported on its proximal side by an extension of the clathrate structure of the stem and bordering the little hole also above mentioned, which extends into the centre of the stem ; surface of the larger stems bluntly microspined. Size of largest specimens 11 inches long by 5 inches broad, and about 1 inch thick or vertically. Locality. Cape of Good Hope, Natal. * Ann. and Mag. Nat. Hist., 1873. Transformation of an entire shell into chitinous structure by the Polype Hydractinin, with short descriptions of the Polypidoms of five other species (PI. 1). The descriptions of G. procumbens, C. spinosa and Clatina ericopsis are taken with only slight alterations from this paper. ON THE STUI i llltE OF CEUATELLA FUbCA (ciUAY). 21 (4) Ccratclla spinusa. (Carter.) Colony procumbent; thickly branched hard flexible of a dark rich red-purple colour. Main branches round, brownish, covered with small, smooth, often subspatulate erect spines. Stem dividing subdichotomously into purple branchlets, which terminate in a Inaptly pointed extremities. Hydrophores the same as in the foregoing species; most prominent in the round branchlets to which they give, en profil, a serrate somewhat sertularian appearance, the teeth of which are inclined forward. Minute structure: Main stems composed of clathrate chitinous fibre, of which the ineshes are more or less oblong, passing into prominent longitudinal lines on the branchlets where they terminate on the backs of the semitubular plates which respectively form the floors of the hydrophores, to which they thus give support. Size of specimen, which is merely a branch 4J inches long by 2 broad. Locality. Port Natal. Mr. Carter adds that " the spines on the surface distinguish this from the foregoing species, add to which its longer and more pointed branches, longitudinally ridged clathrate fibre and rich red-purple colour." Genus. Chitina. (Carter.) Colony erect, bushy, fragili flexible, fawn coloured. Trunk long, hard, irregularly round, composed of many stems united clathrately and obliquely into a cord-like bundle, which divides and subdivides irregularly into branches which again unite with each other in substance (anastomose) when in contact and finally form a straggling bushy head. Hydrophores long clathrate tubular, terminating the ends of the branchlets, or prolonged from some of the proliferous' tubercles which beset the surface of the trunk and larger stems. Minute structure : Composed of clathrate chitinous fibre throughout, whose network is subrectangular and massive in the stems, where there is no difference between the centre and circumference, with the exception that the fibre is stouter in the former or oldest part; hydrophores composed of several longitudinal fibres or ridges lattice-worked together transversely into a tubular form, somewhat contracted at the extremity, in the centre of which is an aperture of the meshwork a little larger than the rest. Height of specimens about 14 inches, trunk about 1 inch in diameter ; hydrophores averaging l-3rd of an inch long by l-60th of an inch in its broadest part and an aperture 1- 90th of an inch in diameter. (5) Chitina ericopsis. (Carter.) The description of the species is the same as that of the genus. Locality. New Zealand. 22 ON THE STRUCTURE OF CERATELLA FUSCA (GRAY). DESCRIPTION OF PLATES. PLATE II. Fig. 1. Ceratella fusca. Life size. The specimen of which this is a drawing was washed up on Flinders Island, Bass Straits. The main stem of the colony springs from a root-like structure made up of intertwined branches. On the left side arises from the roots a very small independent stem. Fig. 2. Transverse section through a portion of the wall of an expanded gastrozooid. Externally is the layer of ectoderm consisting of ciibical cells. The mesoglcea is an extremely thin layer and the endoderm consists of large vacuolate cells with granular protoplasm aggregated at their inner ends which face into the gastral cavity. The nuclei are conspicuous and placed at the same end. Camera. Zeiss E, oc. 2. Ed. ectoderm. End. endoderm. M. mesogloea. Fig. 3. A small portion of the external surface of a branch in the region in which gonophores are numerous to show the external ectoderm containing thread cells and a portion of one of the ccenosarc tubes. In the latter the endoderm forms a definite layer of darkly-stained, small cubical cells. Surrounding this is the ectoderm in contact with the external layer and containing developing thread cells. E. external layer of ectoderm. Eel. e'ctoderm of coenosarc tube. End. endoderm. A. developing thread cells. Sk. skeleton. Camera. Zeiss E, oc. 2. Fig. 3a. Developing thread cells found in the ectoderm within the branches, a. an ectoderm cell in which the micleus is slightly larger than usual and appears homogeneous, b. the nucleus has increased in size, stains very darkly, lies at one end and is surrounded by a clear space. c. the nucleus begins to show a darker spot within it. d. two darkly- staining thread-like structures are present, e. the nucleus (?) does not stain so deeply, and is not siirrounded by a clear space but has a small amount of protoplasm clinging to it; within it at the somewhat pointed extremity can be seen a light line indicating the larger terminal part of the thread, f. the wall of the thread-cell and the thread itself are clear. 9. The fully developed thread-cell. PLATE III. Fig. 4. Portion of a small branch with the zooids expanded. The skeleton is covered by the soft parts but the dark lines indicate the external parts of the chitinous network which show through the soft structures. ON TUB STRUCTURE OF CERATELLA FUSCA (GRAY). 23 Fig. 5. Portion of the skeleton of a somewhat larger branch showing the chitinous network of which it is composed and the little bracket-like hydrophores. (Hy.) x 12. Fig. 6. Highly magnified small portion of a branch seen partly by direct and partly by transmitted light. Two gastrozooids are shown each of which is placed upon a hydrophore. The latter shows prominent ribs which project beyond the margin and arc connected by a thin fenestrated web of chitin. Two male gonophores arise from the cccnosarc and they and the gastrozooids are quite naked. The whole branch is covered by a thin external layer of ectoderm, x 20. G. gastrozooids. Gon. gonophore. E. external layer of ectoderm. Hy. hydro- phore. Hy. 1 web connecting the ribs of the latter. Fig. 7. Transverse section across the body of a gastrozooid. The tentacles are solid with swollen ectoderm ends filled with thread cells. The zooid has been feeding and the endoderm cells are full of little food particles. F. Remnant of small crustacean on which the zooid is feeding. It lies close against the endoderm on one side and the food particles are passing into the interior of the cells. Outline drawn with Camera, Zeiss E, oc. 2. Fig. 8. Transverse section across a gouophore. Mn. endoderm of the manubrium. Sp. sperm cells in the ectoderm of the latter. Ect. ectoderm of the medusa. R. radial canals. Ect. ectoderm of the sub-umbrella surface. Outline drawn with Camera, Zeiss E, oc. 2. PLATE IIIA. Fig. 9. Semi-diagrammatic drawing of a longitudinal section through a small branch. The skeleton is coloured brown the soft parts grey. E. external layer of ectoderm. Gon. gonophore. G. gastrozooid. Hy. hydrophore. Sk. general network of skeleton cut across in various directions. Outline drawn with Camera, Zeiss A*, oc. 2. Fig. 10. Semi-diagrammatic drawing of a transverse section across a good-sized branch. Letters as in figure 9. Ect. ectoderm of endosarc tubes. End. endoderm. Outline drawn with Camera, Zeiss A*, oc. 2. Fig. 11. More highly magnified portion of a branch cut in transverse section. The ectoderm of the gastrozooid is directly continuous with the external layer of the branch and the base of the zooid is continuous with two of the coenosarc tubes. At C. is represented the characteristic feature of the latter crossing over live connecting strands of the chitinous network. C. points at which the soft parts 24 ON THE STKUCTUUE OF CEKATELLA l-'UBCA (GHAY). cross thin connecting strands of the skeleton. E. external layer of ectoderm. Ect. general ectoderm. G. gastrqzooid. Ply. hydrophore. Sk. general skeleton. Outline drawn with Camera, Zeiss A*, oc. 2. Fig. 12. Portion of a longitudinal section of a branch from which arise two gonophores. The latter are cut in longitudinal section. E. external laver continuous with the ectoderm of the gonophore. End. endoderm of the manubrium. Ect. ectoderm. Ect'. ectoderm of sub-umbrella layer of the medusa. G. gastrozooid. M. point at which the ectoderm dips in corresponding to the mouth of the medusa, ft. radial canals. Outline drawn with Camera, Zeiss C, oc. 2. Fig. 13. Longitudinal section of a branch from which another small one arises. In this specimen the skeleton has more than usual a more or less definite arrangement into ribs which run parallel to the length of the branch and are connected by transverse bands. Outline drawn with Camera, Zeiss A*, oc. 2. Fig. 13A. A small portion of the small branch in figure 13 more highly magnified to show the single ccenosarc tube passing along the centre. The ectoderm is irregular. Letters as before. Drawn under Zeiss F, oc. 2, Fig. 14. Portion of a terminal branch devoid of zooids. Up the centre runs a single tube with an internal unicellular layer of endoderm and an irregular ectoderm. The endoderm gives oft' hollow processes which at certain parts (x) come into direct contact with the external ectoderm (E). Further growth of these will probably give rise to the gastrozooids the external layer of the colony thus forming their ectoderm. Drawn under Zeiss E, oc. 2. Trans RS Victoria 1891 Plate L 9 . Fig. 3 rig Jo -.-X CERATELLA FUSCA If 'B Sffjitf t/.K V.'f. (Ji la L NL 14 DAY USE RETURN TO DESK FROM WHICH BORROWED BIOLOGY LIBRARY TEL. NO. 642-2532 This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. i LD21A-6m-7,'75 (S7525L) General Library University of California Berkeley J Jficr. UBl -- x i v or^ \'/A : MAAr _ x - ^'i a m ^ ^gf^ /^ - 5s A A', sSf/? , r' 1 W^s'A X ft r\, x /CN x -