E. W. Berger

“ 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 have, however, no evidence that the fibers from the prism cells extend beyond the prisms in whose axis they lie. The capsule lies very closely applied to the lens, never becoming separated from it in sections, and is, hence, regarded as a secretion from the lens cells. Just what its function may be is difficult to surmise. The proximal complex eye possesses no capsule. I have thought, however, that if the lens should be adjustable, the capsule might [45] serve as a protection to the prisms of the vitreous portion of the retina during the adjusting movements of the lens. ”

“ It is, of course, possible that the pyramid cells are in a stage of structural transition to the long pigment cells, for, besides their pigmentation, they also have like nuclei. Furthermore, I held for a long time with Conant that there may be only two kinds of cells in the retina, but I soon found the pyramids so definitely shown as to leave no doubt but that they represented a third kind of cell. For me it remained to first definitely see all the fibers in the vitreous body as also the pyramids in sagittal sections. ”

“ 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. ”

“ Claus and Conant also describe a small ventral endodermal tract of nerve tissue, which according to Conant is connected with the endodermal nerve tissue found in the region of the radial ganglia.
To sum up, the epithelium of the club and the peduncle is a flagellate sensory epithelium whose flagella are continued through the cells as nerve fibers into the nerve tissue below. A priori, judging from the mass of nerve tissue underlying the epithelium, we should expect the epithelium to be one strictly sensory. What sense it serves is difficult to surmise. ”

“ I here sum up Romanes’ theory in a few words. The ganglia liberate a constant and comparatively weak stimulus, one perhaps about minimal. This stimulus sets off the contractile tissue; but as the tissue contracts and becomes exhausted the constant stimulus becomes, in relation to it, sub-minimal, and it does not contract again until it has recovered and the stimulus is again strong enough to set it off. The ganglionic theory of rhythmic contraction supposes that the ganglia liberate stimuli to the contractile tissue at successive intervals. ”

“ The Simple Eyes.—Since the shape and position of these eyes have already been described (Claus, Schewiakoff, Conant) , I shall not tarry long in this respect. Speaking generally, these eyes are flask-shaped (Fig. 12) , the proximal pair quite so, while the distal pair are drawn out in the transverse diameter of the club. These eyes are invaginations of the surface epithelium and the shape of the cells lining these invaginations is quite like that of the epithelial cells, except that their distal portions (bordering the lumen of the invagination) are heavily pigmented. ”

“ Where the epithelium covers the region of the concretion, the cells become flattened and with the long axis of their nuclei parallel with the surface of the club (Fig. 7) . The same holds true for the corneal epithelium (Figs. 7, 13) .
It is a significant fact that in many places the nuclei form only a single layer, and in such places one cannot speak of spindle-shaped cells. I cannot find any evidence of sensory and supporting cells as Schewiakoff describes. The fact that spindle-shaped cells may exist is simply a physical consequence of their being closely crowded. ”

“ When one pedalium was cut the others contracted, while stroking the outer edge of the pedalia, touching the sensory clubs, or sharply pricking the subumbrella, often produced the same result. (See also Nerve.) The upper part of the subumbrella seemed not so sensitive and more seldom produced the reflex of the pedalia, while the base of the stomach did not give it at all. Stroking the outer edge of the pedalia of Tripedalia cystophora, the second of the two species of Cubomedusæ described by Conant, also caused the pedalia to be contracted inwards. ”

“ Excision of the sensory clubs demonstrates that they are the seat of important ganglionic centers, the removal of which results in temporary paralysis and weakness. That they also are the seat of organs (eyes, network-cells, concretions) that are of importance in [23] giving information in the life of Charybdea, is evident from the reaching motion of the proboscis after the removal of the sensory clubs. ”

“ Upon the removal of lithocyst pulsations continued, but in groups with short pauses. The normal rate of pulsation was twenty-seven to the half minute, while three minutes after the operation it was seventeen, and eleven minutes after, fifteen to the half minute. The tissue connected with a removed lithocyst gave contractions. Placing a Polyclonia in fresh sea-water more than doubled the rate of pulsation, which, however, soon fell to the normal rate, and lower in one instance. In small individuals the rhythm is decidedly more rapid than in those of larger size. ”

“ Finally, as judged by the results in this paper, Charybdea seems to occupy, physiologically, a position intermediate between the Hydromedusæ and the Scyphomedusæ. In its great activity as a swimmer, in its response to light, and in its reflexes it is Hydromedusan, while in the paralysis and recovery following the removal of its marginal bodies, as also in its response with several pulsations instead of one, when a deganglionated bell is stimulated, it is Scyphomedusan. ”

“ I may note here that the muscle fibers under the ectoderm of the pedalia are specially well developed at and near the inner and outer edges, both in Charybdea and Tripedalia. On the flattened sides of the pedalia the muscle fibers are fewer.
When the pedalia were cut off far enough up to remove the interradial ganglia, coördination was not affected and the animal [13] could pulsate well enough but with little progress. (See above under Velarium and Frenula.)
An isolated tentacle is capable of squirming contractions, and when stimulated at either end, it would contract wholly or in part only. ”

“ A piece of the subumbrella cut off and having, so far as I could determine, no connection with ganglia, frenula, or suspensoria, gave contractions. Another piece was not seen to contract.
A small piece of the subumbrella connected with a club can contract. The proboscis can give contractions of itself when cut off with the base of the stomach. Even a cut-off lip can twitch by itself. ”

“ He concludes that while the principal motor centers reside in the lithocysts, other centers doubtless exist that may function vicariously, but that the centers of the margin are more definitely limited to the marginal bodies in the Scyphomedusæ than in the Hydromedusæ, in which the whole margin seems to be replete with centers. He feels positive, furthermore, that no motor centers exist in Aurelia’s margin outside of the marginal bodies (lithocysts) . Eimer’s results are essentially the same as Romanes’, so that for a more detailed comparison of the two, Romanes’ works should be consulted. ”

“ Hesse [13] regards the axial fibers that he describes for the rods in worms as the primitive fibers of Apathy. In this I agree with him, regarding the axial fibers I have described as “Primitivfibrillen.” Further, I believe, if I understand Apathy rightly, that the fibrils described by Patten as extending laterally from the axial fibers correspond to Apathy’s “Elementarfibrillen.”
It is the long pigment cells that are the puzzling element. ”

“ It would seem, furthermore, that my supposition is supported for Charybdea by the fact that the pedalia and tentacles were contracted so as to be brought inside the bell when the velarium was cut. The stimulus of cutting the velarium may be comparable to a stimulus from some object touching it, and thus cause the pedalia and tentacles to come reflexly to aid in capturing or holding the object, a fish, crustacean, or such, to be captured. ”

“ It seems likely that in 1896 he thought the form to be Polyclonia, while for some reason, in 1897, he supposed it to be Cassiopœa. I have examined several specimens of these medusæ brought from Port Antonio and find that they all have twelve marginal bodies and twenty-four radial canals, according to which (V, Haeckel’s System) , they should be Polyclonia. Conant, however, speaks of removing sixteen marginal bodies, which seems to indicate that he had Cassiopœa. A careful classification of this form of medusæ found about Jamaica seems to be a desideratum. ”

“ When I pulled off pieces of its gonads by means of quick jerks, with a small forceps, it would continually reach toward the injured part of its subumbrella. This medusa is generally quite active with its proboscis and can occasionally be seen to reach with it.
Romanes states in one place that the proboscis is not affected by the excision of the margin. This is evidently not the case in Charybdea, in which excision of the sensory clubs (which really belong to the margin—see “Cubomedusæ”) decidedly stimulated the proboscis to active movements. ”

“ That nerve fibrils ramify in ganglion and sensory cells, and may even leave these cells to join those of other cells, has been well demonstrated by Apathy, [6] so that my finding only a single process of the visual cells leading centrad without giving off lateral fibers cannot be a serious objection. Again, fine nerve fibers coming off from the main centrad process of sensory cells in medusæ have been figured by other observers, among whom I mention the Hertwigs. Careful macerations at the seashore would probably demonstrate them for Charybdea. ”

“ 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. ”