c. I take this reticular body to be the centrosphere, and the central

granule in c and d the centrosome. In k, l, m, n, and o (Fig. 20), which are from another series, in which the walls of the nuclei did not stain so dark as in the other nuclei of the same figure, a nucleolus could be definitely seen, indeed, sometimes quite perched upon the wall of the nucleus (k, l). In several instances I could see two nuclei, as in o. But besides these nucleoli, I could in several instances see quite definitely a reticular body (centrosphere) opposite the axis (m, n, o) quite as I described for the nuclei with the dark outlines. In a, b, c, d, e and g the nuclei could not be so readily demonstrated, but I could occasionally see a darker stained body as in a, c and g, that I have no doubt is the nucleolus, which here, again, is perched quite upon the surface of the nucleus. This position of the nucleolus is perhaps due to its having been crowded to one side by the nucleus becoming hollow. It is no uncommon thing, either, to find several nuclei in a single cell, sometimes in process of division or just divided as o and e (Fig. 20), also h, i and j. The whole nuclear phenomenon that I have described seems to be one of division. Perhaps it is somehow associated with the giving off of the secretion of the cells, for these nuclei seem to be found in greatest abundance in those cells in which the secretion is most abundant. In Conant’s sections I found but little evidence of these nuclear phenomena as also little secretion, which all goes to show the association of the nuclear phenomenon with the secretion. I have failed to find any descriptions in the literature of nuclei to which I could refer my observations.

The endothelium of the ampulla is flagellated (Figs. 7, 17, 27). It will be seen that there are two slender flagella to a cell. Each pair of flagella has a pair of basal bodies that are longer than thick, and which are continued as a thin fiber towards the nucleus of the cell. That these centrad continuations of the basal bodies extend to or past the nucleus I could not determine. Sometimes the basal bodies with the centrad continuations are pushed quite to one side of the cell (Fig. 27), while in other cells they are applied quite to the distal surface (Figs. 7, 17, 27). Fig. 17, and the part of Fig. 7 that shows these points, are taken just through the tips of the cells. The darker lines within the polygonal areas are the intracellular basal bodies with their centrad continuations, while the thinner lines are the flagella, and are supposed to lie in the plane just below the plane of the figure. In those instances in which the centrad continuations are applied to the distal surface of the cells they could occasionally be seen to bend centrad (Fig. 27b). While these cilia with their basal bodies and centrad continuations are usually separate, as shown in the figures, yet they are at times applied quite closely to each other so that the double nature of the basal bodies and their centrad continuations is not evident. When the intracellular continuations of the cilia become pushed to one side or applied to the distal surface of the cells, I believe this to be due to the turgor of the cells consequent upon the deposition of large masses of secretion within them. But I must add that this explanation is not altogether satisfactory, since in the endoderm cells of the pedalia of both Charybdea and Tripedalia I found like conditions with no evidence of a secreting function. (See below, under tentacles.) No one, to my knowledge, has described the flagellation in detail, although both Claus and Schewiakoff state that the endoderm is ciliated.

The “floating cells” in the stomach pockets and in the ampulla, described by Conant, I believe are in part derived from the endothelial cells of the ampulla. That a portion of them may arise from the ovary, as Conant explains, I do not doubt; I have, further, found a mass of floating cells in a small Charybdea quite as Conant describes for Tripedalia (his Fig. 71). In this Charybdea, however, I could find no traces of any ovary. Conant speaks of larger and smaller floating cells, and that the smaller ones are also found in the males. This latter fact agrees with what I have suggested, that some of the floating cells arise in the ampulla. My chief reasons for my supposition, however, are the following: I find globules of the secretion of the ampulla cells in some of the floating cells and also scattered loosely among them (Fig. 19). These globules in and among the floating cells have the same general appearance and a similar staining capacity as the secretion in the ampulla cells. Again, in spaces within some of the ampulla cells I find bodies resembling the floating cells with lumps of the secretion within them (Fig. 18). The conclusion, therefore, lies near that some of the floating cells originate within the cells of the ampulla, engulf within them some of the secretion, and are then expelled into the lumen of the ampulla. Better said, perhaps, they represent portions of the ampulla cells with some of the secretion. I also found several instances in which a floating cell had the appearance of being expelled from an ampulla cell. Conant suggests for a similar observation that the cells were about to be swallowed by the ampulla cells. I believe, however, that my finding a secretion similar to that within the cells of the ampulla, in some of the floating cells, as also bodies very much like them and filled with secretion within the ampulla cells, together with Conant’s finding floating cells in males, and finally the observation that the floating cells are usually quite dilapidated, never showing a healthy cell structure--all this leads me to conclude that some of the floating cells originate from the ampulla cells, and that they have a nutrient function in distributing the secretion. This is quite the reverse of what Conant supposed,--that they were taken in as nourishment by the ampulla cells. I also find what appears to be a secretion in the endoderm of the tentacles of both Charybdea and Tripedalia, and believe this is another source of the floating cells. (See below, under tentacles.)

I also found other very darkly staining bodies (Fig. 19) both within the floating cells and free in the ampulla cavity, and more numerous in the ampulla cells themselves. This again goes to show that floating cells take their origin from the ampulla cells. What these darkly staining bodies are, I cannot say. Perhaps they are something akin to the “Chromatoider Nebenkörper” described by Lenhossek (L), or they represent another kind of secretion. If these floating cells are derived from the cells of the ampulla, the active nuclear division within these also receives an explanation. Some nuclear matter can usually be observed in the floating cells.

_The Endothelium of the Peduncle._--The endothelium of the peduncle consists of flagellate columnar cells (Fig. 27, upper half). The cells are vacuolated at their bases like some of the cells of the ampulla, and contain a comparatively large nucleus with nucleolus. The flagella are long and slender, quite like those described for the cells of the ampulla, except that there is only one to each cell. The basal bodies of the flagella are of a peculiar shape. They may be described as a bent spindle, continuous at their distad ends with the cilia and at their centrad ends with a fiber that can be traced quite to the neighborhood of the nucleus. I could not trace these fibers into the basal parts of the cells, except in one instance, and I could not be sure of that (Fig. 27a).

Another interesting observation in connection with the basal bodies is that they are bent in one direction on one side of the canal and in an opposite direction on the other side. In Fig. 27, which represents a longitudinal section of the endoderm and the supporting lamella of the dorsal (_i. e._ farthest from the eyes) side of the peduncle, the distal ends of the basal bodies are bent towards the ampulla, while on the ventral side they would be bent away from the ampulla. This seems to suggest that the flagella move the contents of the canal in one direction on the dorsal side of the canal and in an opposite direction on the ventral side. Conant observed in living material that bodies in the ampulla and the canal were moving about, and that bodies within the tentacles were moving in opposite directions at the same time. This last observation and the histological facts just described, I believe, are mutually corroborative. Again, _a priori_, we should expect some such mechanism as the one described to bring about an exchange between the contents of the ampulla and that of the stomach pockets. I have not as yet been able to demonstrate a similar flagellate mechanism in the tentacles. Flagella and basal bodies are present in the tentacles, but I could not determine that the basal bodies had any definite arrangement like that shown in Fig. 27. (See under tentacles.) I may add, yet, that the cells in the canal of the manubrium have cilia, similar to the ones just described, with large basal bodies, and with centrad continuations. Finally, I am not certain but that these cells form buds at their ends quite like those I describe for the endothelial cells of the tentacles (see below), and that they aid in the formation of the floating cells. I thought I saw such buds just at the entrance of the lumen of the peduncle into the ampulla, but could not find conclusive evidence.

_The Tentacles and the Pedalia._--My observations on the tentacles were begun with the object of demonstrating a flagellate mechanism similar to the one described above for the endothelium of the peduncle. While I have failed to demonstrate such a mechanism for the tentacles, yet several interesting points came to my notice. It will be remembered that the tentacles of the Cubomedusæ are not directly attached to the bell, but that a blade-like portion, the pedalium, intervenes between the tentacles and the bell. For figures of the pedalia and the tentacles the works of Haake, Claus, Conant and Maas[22] may be consulted.

_The Ectoderm._--The ectoderm of the tentacles is the seat of a number of differentiations. It is quite thick, as the figures (28 and 29) show, and in this respect is very different from the pedalia, on which the ectoderm cells are quite cubical. I found evidence of cilia here and there, but I can add nothing definite about them. Neither can I add any definite statements regarding the ectoderm cells proper, but what I have to say relates to their differentiations.

(a) The _thread cells_ are of two kinds, larger ones and smaller ones. This is well shown in Fig. 29, which is part of a transverse section of a tentacle of Tripedalia. Two kinds of nettle-cells are also present in the tentacles of Charybdea, but they were specially well shown in Tripedalia. The structure of these thread-cells seems to be typical, and I have little more to say about them. I wish, however, to call attention to the five or six unstriped muscle-fibers that are attached to their basal lateral parts, and which connect them with the basement membrane (Figs. 28, 29). Claus describes these muscle-fibers and mentions that Fr. Müller has described them before him, but I have not found them mentioned elsewhere in the literature of nettle-cells. Professor Brooks tells me, however, that he has often found them. It would appear from Fig. 29 that they serve to retract the thread-cells from the surface. Claus suggests that the muscles are developed from the cnidoblasts.

(b) The plain subectodermal _muscle-fibers_ are of interest. In Charybdea they lie wholly enclosed within canals of the supporting lamella (Fig. 32, upper part). They run longitudinally, and near the base of each tentacle pass out of their canals and become strictly subectodermal (Figs. 31, 32). This is for Charybdea. In Tripedalia they rarely come to lie in closed canals as in Charybdea. These facts show beyond doubt that these muscles are developed from the ectoderm. Claus has suggested their ectodermal origin, but did not demonstrate it. He also suggested that they become inclosed in canals by the supporting lamella pushing up around them and finally fusing above them. This, I believe, is demonstrated by the conditions in Tripedalia (Fig. 29). Here the canals usually remain open, but occasionally, as in the left-hand canal, one may become completely inclosed. This condition of things suggests the intra-lamellar muscles found in actiniarians. The nuclei found in the canals with the muscle-fibers probably belong to the cells from which the muscles become differentiated. Claus figures these muscle-fibers and nuclei, and it may be added that the supporting lamella he figures, for C. marsupialis, is much thicker than I have figured it for C. Xaymacana and Tripedalia cystophora. The number of muscle-canals also is greater and occupies a much greater depth of the thickness of the lamella. Since Claus gives a figure of a transverse section showing the muscles in their enclosed canals, I have not deemed it necessary to duplicate his figure. In the transition from a tentacle to a pedalium, the muscles are most strongly developed toward and at the edges of the pedalium. This is true for the pedalia in general, and accounts for the readiness with which they can be bent inwards, as noted in the physiological part of this paper.

(c) I have found a single _ganglion-cell_ among the cells of the ectoderm of the tentacles. This showed so plainly that I have figured it (Fig. 28). Other ganglion-cells no doubt exist, but could probably not be distinguished from other cells. In its position in Fig. 28 it appears to be associated with the nettle-cell shown just above it. Its position is very much the same as that figured by Lendenfeld (25a).

_The Endoderm._--The cells of the endoderm of a tentacle are long and quite slender (Fig. 31). At their bases they are vacuolated quite like the cells of the ampulla and the canal of the sensory clubs. They contain a well-formed nucleus with a nucleolus. In their distal half small light bodies with a dark center are very evident. These bodies are evidently a secretion.

Another peculiar phenomenon presents itself in these cells. The distal part of each cell becomes separated off from its body by what appears to be the formation of a transverse cell-wall (Fig. 31, c-d). I have found the ends of these cells quite separated off in some series. The formation of the walls seems to begin as a thickening at the sides of the cells, and a section through this region, transverse to the cells, would appear like Fig. 30. The dots in the centers of the polygonal areas of this figure are the centrad continuations of the cilia to be described below. As already remarked in describing the endoderm of the ampulla, I believe we here have another place of origin of the “floating cells.” The secretion just described moves into the distal parts of the cells prior to their separation (Fig. 31). In some series I could see these secretion bodies much more numerous within the distal ends of the cells than in Fig. 31.

As will be seen in Fig. 31, each of the endoderm cells of the tentacles has a flagellum that extends into the lumen of the tentacle. Each flagellum has a thickening just within its cell, which may be regarded as a basal body. From this basal body, again, a small fiber extends centrad into each cell. It does not appear that the flagella are thrown off with the distal parts of the cells; at all events, I never found them connected with any of the floating cells except in a few doubtful instances.

What I have said for the endoderm of the tentacle of Charybdea applies equally to Tripedalia.

Claus, in his figure of a transverse section of a tentacle of C. marsupialis shows the endoderm as cubical. I cannot explain why there should be such a difference between the endoderm of the tentacles of _C. marsupialis_ and that of the tentacles of _C. Xaymacana_ and _Tripedalia cystophora_. Claus does not describe the endoderm in detail.

The endoderm cells of the pedalia of both Charybdea and Tripedalia are cubical and possess flagella, basal bodies, and centrad continuations, quite like those I have described for the endoderm cells of the ampulla. The double nature of the basal bodies and the centrad continuations is, however, not so evident. A secretion I did not find. Histologically, therefore, the endothelium of the pedalia corresponds rather with that of the ampulla, and that of the tentacles with that of the peduncle of the clubs.

SUMMARY.

The most important results in the histological part of this paper relate to the structure of the retinas of the eyes of the sensory clubs.

The retina of the distal complex eye is composed of three kinds of cells: two kinds of sensory cells (the prism and pyramid cells), and the long pigment cells (Figs. 1-9). The prism and pyramid cells have each an axial nerve fiber in their prisms and pyramids respectively. These fibers I could, however, trace only to the neighborhood of the nuclei. But since I could trace similar fibers in the retinal cells of the simple eyes (Fig. 16) past the nucleus into the subretinal nerve tissue, I believe that the axial fibers in question also extend centrad as nerve fibers into the subretinal nerve tissue. Other observers also figure such fibers as extending centrad as nerve fibers. The axial fibers of the prism cells have each a dumbbell-shaped basal body at their entrance into the pigmented part of a cell. The evidence for a body of such shape in the pyramid cells was not conclusive, though a basal body for the axial fiber exists. The long pigment cells project or retract their pigment in light or darkness respectively and thus seem to serve to check the diffusion of light in the retina. I have also supposed that these cells may serve for conducting impulses to the lens, and that the latter is adjustable.

The proximal complex eye (Fig. 13) has only the prism cells present in its retina, and not two kinds of cells as Schewiakoff has described (see text, pp. 53, 60, 63) for all the eyes.

The simple eyes (Fig. 12), two on each side of a club, four in all, also have only one kind of cells in their retinas, and each cell has a flagellum extending into the vitreous secretion of the lumen. These flagella could be traced centrad as a nerve fiber (Figs. 12, 16). Similarly, a nerve fiber could be traced centrad from the flagella of the epithelial cells of the clubs. Dumbbell-shaped basal bodies for the flagella of the simple eyes could also be demonstrated, but the evidence for this in the epithelial cells of the clubs was not so satisfactory.

Other points of interest are: A secretory epithelium lining the ampulla of the clubs, and a somewhat similar epithelium lining the canals of the tentacles (Figs. 7, 27, 31); the partial origin of the “floating bodies” in the canals of the clubs and tentacles and the stomach pockets from these epithelia (Figs. 18, 19); two flagella to each cell of the endothelium of the ampulla and of the pedalia (Figs. 7, 17); the peculiar nuclei in the endothelial cells of the ampulla (Fig. 20); the longitudinal muscles of the tentacles being completely inclosed within canals of the supporting lamella, but near the base of a tentacle becoming subectodermal. This demonstrates their ectodermal origin. In Tripedalia it is seldom that any of these muscles become enclosed as in Charybdea (Fig. 29).

If to the reader my results seem to embody a somewhat heterogeneous detail, he must remember that the work consists partly in corroborating and partly in supplementing the work of previous observers, and that, in general, histological detail does not usually make the most readable paper.

BIOLOGICAL LABORATORY, JOHNS HOPKINS UNIV., May 1899.

FOOTNOTES

[a] It was at one time supposed that the concretions in the marginal bodies of medusæ represented lenses and the surrounding nerve tissue the optic nerve, a supposition so highly improbable that it never gained any acceptance. (Ib., p. 41, note.)

[b] Eimer’s results I get from Romanes and Hesse[III].

[c] By no means do I wish to attribute intelligence to these animals.

[d] Haake[2] says that in the adult _Charybdea Rostonii_ the vitreous bodies of the complex eyes are absent but present in the young. It is difficult to explain this observation except on grounds of imperfect preservation of the adult material, for in all observations on other forms a vitreous body is described. Haake evidently did not use sections, and for this reason his results must be regarded as of doubtful accuracy. Haake also says that the simple lateral eyes of the clubs are absent in the adult, but present in the young.

[e] In the series from which Fig. 3 is taken the pyramid-cells are not so readily demonstrated. Indeed, I missed them altogether at first in this and some other series and supposed that there were only two kinds of cells (19), but upon a careful re-examination I could demonstrate them to my satisfaction. They did not show, however, in the particular section of Fig. 3, so that they are not indicated in this figure.

[f] I go into this at some length because the cell-walls in the series that showed the nuclei best differentiated as lighter and darker ones did not show well, and there might be some doubt that these lighter nuclei belonged to the pyramid cells. I could, however, in many instances, trace the axial fibers of the pyramids through the pigmented zone to these lighter nuclei (as already noted) which fact can leave no doubt but that some of these nuclei belong to the pyramid cells. (Similar nuclei, however, are found to belong to the long pigment cells, to be described below.) Centrad these pyramid cells are continued into a single process just as the prism cells were shown to be (Fig. 7). Figures 6, 8, 9, and 21 show samples of all the pigmented cells found in macerated preparations, and none of these (except Fig. 9, long pigment cells) show more than a single centrad process. Hence, I conclude that centrad both the pyramid cells and prism cells are continued as a single prolongation.

[g] I have been able to demonstrate nucleoli in all the different nuclei of the cells of the sensory clubs.

[h] It may be objected that my criterion, the presence of axial fibers, is not necessarily characteristic of visual cells. However, the great general occurrence of such axial fibers (Patten,[5] Grenacher,[16] Schreiner,[12] Hesse,[13] myself, in simple complex eye, see below, and perhaps others) in eyes in which the retina has only one kind of cells, would seem to indicate that they are quite characteristic of visual cells. Note again that in the proximal eye of Charybdea there is only one kind of cells and with axial fibers.

[i] Mr. J. C. Olsen, of the Chemical Laboratory, kindly made these tests for me.

LITERATURE.

LITERATURE REFERRED TO IN THE SECTION ON PHYSIOLOGY.

I. ROMANES, G. J. a. ’75, ’77. The Locomotor System of Medusæ. Philosophical Transactions. London. Vol. CLXVI, pt. 1. Vol. CLXVII, pt. 2.

b. ’85. Jelly-fish, Star-fish and Sea-urchins. London.

II. MURBACH, LOUIS. ’95. Preliminary Notes on the Life-history of Gonionemus. Journal of Morphology. Vol. XI.

III. HESSE, R. ’95. Über das Nervensystem und die Sinnesorgane v. Rhizostoma Cuvieri. Zeit. Wis. Zool., B. LX.

IV. EIMER, TH. Zoologische Untersuchungen. ’74. Würzburg Verhandlungen. VI. Bd.

V. HAECKEL, E. ’79. Monographie der Medusen. Jena.

VI. BERGER, E. W. ’98. Abstract of Dr. F. S. Conant’s Notes on the Physiology of the Medusæ. Johns Hopkins University Circulars. Vol. XVIII, No. 137.

VII. (See also 8, below.)

LITERATURE REFERRED TO IN THE SECTION ON HISTOLOGY.

1. CARRIÈRE, J. ’85. Die Schorgane der Thiere. München u. Leipzig.

2. HAAKE, W. ’87. Scyphomedusen des St. Vincent Golfes. Jen. Zeit. f. Naturwis., Bd. XX., pp. 596-597, 602-604.

3. CLAUS, C. ’78. Über Charybdea marsupialis. Arb. aus dem Zool., Inst. Univers. Wien., Bd. I.

4. SCHEWIAKOFF, W. ’89. Beiträge zur Kenntniss des Acalephenauges. Morph. Jahrb., Bd. XV, H. 1.

5. PATTEN, WILLIAM. a. ’89. Studies on the eyes of Arthropods. II. Eyes of Acilius. Journal of Morphology. Vol. II.

b. ’98. A Basis for a Theory of Color Vision. American Naturalist. Vol. XXXII, No. 383.

6. APATHY, ST. ’97. Das Leitende Element des Nervensystems u. seine topographischen Beziehungen zu den Zellen. Mitt. Zool. Stat. Neapel., Bd. XII, H. 4.

7. PARKER, G. H. ’97. Photomechanical Changes in the Retinal Pigment Cells of Palæmonites, and their Relation to the Central Nervous System. Bull. Mus. Comp. Zool. Harvard Coll. Vol. XXX, No. 6.

8. CONANT, F. S. a. ’97. Notes on the Cubomedusæ. Johns Hopkins University Circulars. Vol. XVII, No. 132.

b. ’98. The Cubomedusæ. Memoirs Biological Laboratory Johns Hopkins Univ. Vol. IV, No. 1.

9. A REVIEW OF 5b. ’99. A Theory of Color Vision. Natural Science. Vol. XIV, No. 85.

10. HERRICK, F. H. ’91. The Embryology and Metamorphosis of the Macroura (Brooks and Herrick). Natl. Acad. Sciences. Vol. V, p. 454.

11. HERTWIG, O. & R. ’78. Das Nervensystem und die Sinnesorgane der Medusen. Leipzig.

12. SCHREINER, K. E. a. ’96. Die Augen bei Pecten und Lima. Bergens Museums Aarbog.

b. ’97. Histologische Studien über die Augen der freilebenden marinen Borstenwürmer. Bergens Museums Aarbog.

13. HESSE, R. ’99. Untersuchungen über die Organe der Lichtempfindung bei niederen Thieren. V. Die Augen der Polychäten Anneliden. Zeit. Wis. Zool., B. LXV, H. 3.

14. ANDREWS, E. A. ’92. On the Eyes of Polychætous Annelids. Journal of Morphology. Vol. VII.

15. WILSON, H. V. ’78. Unpublished Notes.

16. GRENACHER, H. ’84. Abhandlungen zur vergleichenden Anatomie des Auges. I. Die Retine der Cephalopoden. Abhandl. der Naturf. Gesellsch. zu Halle. Bd. XVI.

17. BEER, THEODORE. ’98. Die Accomodation des Auges in der Thierreihe. Wiener klinische Wochenschrift. Nr. 42.

18. WILSON, E. B. ’96. The Cell.

19. BERGER, E. W. ’98. The Histological Structure of the Eyes of Cubomedusæ. The Journal of Comp. Neurology. Vol. VIII, No. 3.

20. LENDENFELD, R. Die Nesselzellen der Chidarier. (Review and bibliography.) Biol. Centralbl. Bd. XVII, Nr. 13.

21. SCHNEIDER, K. ’90. Histologie von Hydra fusca mit besonderer Berücksichtigung des Nervensystems der Hydropolypen. Arch. Mik. Anat. Vol. XXXV.

22. MAAS, O. ’98. Die Medusen. (Charybdea arborifera, Systematic.) Mem. Mus. Comp. Zool., Harvard Coll. Vol. XXIII, No. 1.

LITERATURE REFERRING TO THE CENTRAD CONTINUATIONS OF CILIA AND FLAGELLA.

A. HAECKEL, E. ’72. Die Kalkschwämme. Vol. I, p. 141; Vol. III, Pl. 25, Figs. 3-5.

B. SCHULTZE, F. E. ’75. Rhizopodien Studien. V. Arch. Mik. Anat. Bd. II, p. 583.

C. EIMER, TH. ’77. Weitere Nachrichten über d. Bau des Zellkerns, nebst Bemerkungen über Wimperepithelien. Arch. f. Mik. Anat. Bd. XIV, Taf. VII, p. 114.

D. BÜTSCHLI, O. ’78. Beiträge zur Kenntniss der Flagellaten, u. s. w. Zeit. f. Wis. Zool. Bd. XXX, p. 269.

E. ENGELMANN, TH. W. ’80. Zur Anatomie u. Physiologie d. Flimmerzellen Pflüger’s Arch. Bd. XXIII.

F. HATSCHEK, B. ’85. Entwickelung der Trochophora von Eupomatus uncinatus Arb. Zool. Inst. Wien., Bd. VI, p. 139.

G. HEIDER, K. ’86. Zur Metamorphose der Oscarella lobularis. Arb. Zool. Inst. Wien., Bd. VI, pp. 189-194.

H. SCHNEIDER, K. C. ’92. Einige histologische Befunde an Coelenterata. Jen. Zeit. f. Nat. 27, N. F. 20.

I. HECHT, EMILE. ’95. Contribution a l’Étude des Nudibranchs. Memoirs de la Société Zool. de France. T. 8, Pl. IV, Fig. 45.

J. MINCHIN, E. A. ’96. Notes on the Larva and Postlarval Development of Leucolosolemia variabilis, etc. Proc. R. Soc., London. Vol. LX.

K. HENNEGUY, L. F. ’98. Sur le rapports des ciles vibrales avec les centrosomes. Arch. d’anat. micros., T. 1.

L. LENHOSSEK, H. ’98. Über Flimmerzellen. Anat. Anz. (Supplement.) Bd. XIV.

M. PETRE, CARL. ’99. Das Centrum für die Flimmer u. Geisel-bewegung. Anat. Anz. Bd. XV, Nos. 14 and 15.

N. See also 6.

REFERENCE LETTERS.

a = flagellum in Fig. 27, that is supposed to extend centrad beyond the nucleus.

b = twin flagella in Fig. 27, of which the centrad continuation is seen applied against the distal surface of the cells and to be continued centrad.

c = capsule of lens.

cf = axial fibers of cells extending centrad.

co = cornea.

concr = concretion cavity.

ec = ectoderm.

en = endoderm.

f = flagella.

flp = distal fiber of a long pigment cell.

fpr = axial nerve fiber of a prism cell.

fpyr = axial nerve fiber of a pyramid cell.

frc = axial nerve fiber of the retinal cells of the simple eyes.

gc = ganglion cells.

ind = impression of the lens probably due to the pressure of weight against the surrounding tissue.

l = lens.

lp = long pigment cells.

m = muscle fibers.

namp = nuclei of ampulla cells.

nc = network cells (Figs. 13 and 16), and nettle cells (Figs. 28, 29).

nf = nerve fibers and tissue.

nlp = nucleus of long pigment cell.

nm = nucleus of muscle cells.

nprc = nucleus of prism cell.

npyrc = nucleus of pyramid cell.

nz = nuclear zone.

pr = prism of prism cell.

prc = prism cell.

pyr = pyramid of pyramid cell.

pyrc = pyramid cell.

pz = pigmented zone.

r = retina.

s = secretion in endo. of tent. and ampulla.

sh = shrinkage space.

sec = vitreous secretion in the lumen of the simple eyes.

sla = supporting lamella.

vb = vitreous body or zone.

x = (1) the approximate level at which Fig. 4 should be cut transversely to give Figs. 1 and 3.

(2) the thickening of the supporting lamella in Fig. 13 to support the lens.

* = Point of approximation of cells of lenses in Figs. 7 and 13.

DESCRIPTION OF FIGURES.

ALL FIGURES, UNLESS OTHERWISE STATED, ARE FROM CHARYBDEA.

Fig. 1. This figure represents a transverse section through a portion of the vitreous body of the distal complex eye at about the level x of Fig. 4. Three kinds of areas are seen, namely, the prisms and pyramids with their axial fibers and the distal continuations of the long pigment cells. Towards the lower left of the figure the section is a little more distal than at the right and the transverse areas of the long pigment cells are no more so large as at the right of the figure. The dark granules in the areas of the long pigment cells represent pigment. Camera lucida sketch. ×920. pp. 45, 46, 48, 49, 50, 51, 52, 54.

Fig. 2. This figure is a camera lucida sketch from a section taken transverse through the most distal part of the pigmented zone of a slightly pigmented retina of a distal complex eye. The presence of three kinds of elements is again evident. The dots without the polygonal areas represent the centrad continuations of the axial fibers of the prism cells. The lettering explains the other areas. ×920. pp. 46, 48, 50.

Fig. 3. This is from a section similar to that of Fig. 1, but a little more distal. At the right, the section is more distal than at the left of the figure, in consequence of which the long pigment cells are there taken through their distal fibers. Note the small shrinkage spaces about the axial fibers of the prisms. The white lines bounding the prism areas appear as in nature. The pyramid cells are not shown in this figure. ×950. Camera sketch. pp. 50, 51, 52, 54.

Fig. 4. This figure is from a section taken parallel to the long axis of the cells of the retina of a distal complex eye. It is from a camera sketch, and nothing has been put into the figure except what could be clearly seen. The lateral boundary lines of the prisms are not shown. Note the evidence for the existence of three kinds of cells. ×920. pp. 44-52, 54.

Fig. 5. This figure represents a sagittal section through the nuclear and pigmented zones and the subretinal nerve tissue of a slightly pigmented retina of a distal complex eye, that had been killed in the dark. Camera sketch. The pyramid cells are not shown. ×900. pp. 47, 51, 52, 53.

Fig. 6. These cells are from a preparation by Conant of a sensory club, macerated in acetic acid. Cell a is evidently an iris cell. The others are probably prism cells from the proximal complex eye. ×900. pp. 44, 48.

Fig. 7. In this figure I represent a sagittal section through the distal complex eye. In the middle half of the section, the nuclei, the prism and pyramid cells with their axial fibers, and the long pigment cells with their large distal fibers are all strictly camera lucida sketched. A portion of the pigmented zone has been left unpigmented to better show its structure. At the right and above the concretion cavity is shown a portion of the endoderm of the ampulla. The section is not strictly in a dorsoventral plane of the club, in consequence of which the cells of the ampulla are cut diagonally and through their tips. Note the dumbbell-shaped nuclei of the ampulla cells, as also the masses of secretion. A part of the retina of the proximal complex eye is shown in the upper part of the figure. ×920. pp. 41-54, 63, 64, 68-71.

Fig. 8. These cells are from a macerated preparation. Cells a, b, c, d may be either prism or pyramid cells from the distal complex eye or prism cells from the proximal complex eye. Cells e and f are probably from the right fourth (Fig. 13) of the retina of the proximal complex eye or from the simple eyes. The unlettered cells are probably from the simple eyes. Some of these show a distal process. ×900. pp. 48, 62, 65.

Fig. 9. The cells here figured are long pigment cells from the same preparation as Fig. 6. ×900. pp. 50, 51.

Fig. 10. This drawing shows an end view of a group of prisms from the same preparation as Fig. 6. ×900. pp. 46.

Fig. 11. This group of prisms are from the same preparation as Fig. 6. Two of them are broken off. The fibers seen at the lower end are probably some of the axial fibers. The fiber at the upper end I believe is interprismatic and the distal fiber of a long pigment cell. ×900. pp. 46.

Fig. 12. This figure is a summary of my results on the simple eyes. It is from a camera sketch of one of the distal eyes, but somewhat diagrammatic. The left side of the figure is proximal, the right side distal. ×920. pp. 61, 62, 64, 65.

Fig. 13. Sagittal dorsoventral section of a proximal complex eye. Conant drew and published this as his Fig. 69. Conant’s evidence regarding the axial fibers of the prism cells was incomplete; so that, in this respect, he left his figure unfinished. I have drawn in these fibers and republish the figure. At the right of the retina and next the lens (the white space) the vitreous body is incomplete and the fibers from the retinal cells project freely into the space. This part of the retina also remains unpigmented. Like my Fig. 7, this figure evidently represents a section somewhat to one side of a sagittal dorsoventral plane of the club, so that the endoderm cells of the ampulla are cut diagonally or transversely. pp. 41-44, 60, 64-68.

Fig. 14. This is drawn to show how regularly small shrinkage spaces may occur in transverse sections of the vitreous bodies. This figure is from a transverse section of the vitreous body of a proximal complex eye. I believe that these spaces are determined by the axial fibers of the prisms. Prism outlines are not shown. ×950. pp. 54.

Fig. 15. This figure is a drawing of a portion of a transverse section of one of the simple eyes. Note the flagella from the retinal cells. pp. 62.

Fig. 16. The section of the lower left hand corner of this figure is through a portion of one of the proximal complex eyes, and shows the centrad continuation of the axial nerve fibers of the retinal cells. The section is such, that, besides the simple eye, the nuclei of the proximal complex eye (upper part of figure) and two network cells are cut. ×920. pp. 47, 62, 63.

Fig. 17. A transverse section through the tips of the ampulla cells is here shown. To the left is towards the upper end of the ampulla. The basal bodies with the centrad fibers are in the plane of the section, while the flagella are supposed to extend below the plane of the section. ×1350. pp. 71.

Fig. 18. These bodies, from within the ampulla cells, contain some of the secretion of the ampulla cells, and resemble the “floating bodies.” ×1350. pp. 72.

Fig. 19. The “floating bodies” here represented are from the ampulla. Globules of a secretion similar to that found in the ampulla cells are seen both within and without the bodies. Note also the two black bodies without the cells and two or three similar ones within the cells. These latter bodies are of doubtful nature. ×1320. pp. 72.

Fig. 20. This figure represents sections of the various nuclei found within the ampulla cells. ×1350. pp. 69, 70.

Fig. 21. These cells are from the same preparation as Fig. 6. They are evidently retinal cells from the simple eyes. The tendency of their pigmented ends to become globular, I believe, is due to their having become isolated before they hardened during maceration. ×920. pp. 62.

Fig. 22. This diagram illustrates the retraction of the long pigment cells. The dotted lines in the vitreous body mark the outlines of the prisms, while the continuous lines represent the axial fibers of the prism and pyramid cells. pp. 45, 46, 48, 49, 53.

Fig. 23. These cells are from the epithelium of a sensory club. They are from the same preparation as Fig. 6. Flagella are not shown. ×900. p. 64.

Fig. 24. This group of epithelial cells of a club are from the same preparation as Fig. 6. ×850. p. 64.

Fig. 25. This sketch is a transverse section through the tips of the epithelial cells of a club. The polygonal areas are the cells, while the central dots are the centrad continuations (nerve fibers) the flagella of the cells. ×920. pp. 63, 65, 66.

Fig. 26. The flagella of the epithelium of a club are in this figure seen to extend centrad, some beyond the nuclei. Cell outlines are not shown. ×920. pp. 64, 65, 66.

Fig. 27. The cells of the lower half of this figure belong to the ampulla, those of the upper half to the canal of the peduncle. The right side of the figure is towards the eyes (the ventral side) of the club. Globules of secretion are seen within the ampulla cells, as also a globule without. The ring above the latter globule is probably an empty shell of a floating cell. ×1320. pp. 68, 69, 71, 73.

Fig. 28. This figure is from a transverse section of a tentacle of Charybdea. The mass with darkly stained granules is the remains of a thread cell. The ectoderm and a small part of the supporting lamella only are figured. Note the large ganglion cell. ×920. pp. 74, 75.

Fig. 29. Part of a transverse section of a tentacle of Tripedalia. The endoderm is not figured. The supporting lamella is seen to be considerably thinner than in Charybdea. Note the subectodermal muscles, as also the muscle fibers to the thread cells. ×920. pp. 69, 74, 75.

Fig. 30. This is a transverse section through the endothelium of a tentacle of Charybdea in the line c d of Fig. 32. The dark lines bounding the polygonal areas are the thickenings of the sides of the walls of the cells in the line indicated. The central dots are the centrad continuations of the flagella. ×920. p. 76.

Fig. 31. This figure is a transverse section through a tentacle of Charybdea at about the middle of Fig. 32, _i. e._ so near to where the tentacle joins the pedalium, that the muscles within the lamella have all come to lie under the ectoderm. The ectoderm is not shown. ×920. pp. 75, 76.

Fig. 32. A longitudinal section through the supporting lamella only, of a tentacle of Charybdea, is here shown. In the upper part of the figure the muscle fibers are seen wholly enclosed by the supporting lamella. In the middle of the figure they are seen to pass out of their canal. In the lower part of the figure, the supporting lamella is seen to bend to the right where it becomes continuous with the lamella of the pedalium. ×920. p. 75.