10. Floating and Wandering Cells. In the stomach pockets, the canals of the sensory clubs, and even in the stomach itself, are found in varying numbers freely floating cells having the appearance of young ova. They vary in size, the smallest being of the size and having the general aspect of the small ovocytes found in the ovary. The largest ([Fig. 70]) have exactly the same structure as the young ovarian eggs before they have begun to accumulate yolk. The granular deeply staining cytoplasm, the clear non-staining nucleus with its bright nucleolus and the nucleolus-like yolk nucleus, all show beyond doubt that these freely floating cells originate in the ovary.
In some of my preparations these cells are found not only floating free, but wandering through the tissues. [Fig. 70] shows two such wandering cells fixed just as they were making their way either through the digestive epithelium into the gelatine of the floor of the stomach, or from the gelatine into the epithelium. The former seems the more probable, though why they should want to get into the gelatine is not very easy to conceive.
Perhaps there is some connection between this and the appearance that the young ovarian eggs have of pushing their way from the epithelium into the gelatine of the ovary. And of course it is not impossible that the whole phenomenon is abnormal, due to rupture of the ovaries which sets free young ova to exhibit their amœboid tendencies under new conditions. Against such an explanation, on the other hand, might be urged the fact that what seem to be the small floating cells are found occasionally in males as well as females, and that in the females a series can be traced with a good degree of certainty between the small floating cells like those found in the walls, and the larger ones which have all the characteristics of young ova.
However that may be, this amœboid action of cells having the structure of ova brings to mind the remarkable form of asexual reproduction described by Metschnikoff for Cunina proboscidea, under the name of “Sporogonie.” Unfortunately Metschnikoff’s original paper was not accessible to me, so that I was unable to obtain more particulars on the subject than those given in Korschelt and Heider’s text-book (p. 33). The reproductive organs of both males and females of Cunina proboscidea are said to produce, besides the usual distinctively sexual elements, neutral amœboid germ cells, which wander into the endoderm of the stomach and circular canal, and also penetrate into the gelatine of the subumbrella. These amœboid cells divide parthenogenetically. One of the two cells of the first cleavage continues to divide and eventually forms an embryo of Cunina; the other remains amœboid and serves for movement, attachment and nourishment of the embryo.
Charybdea, however, has shown no sign of any such reproductive process on the part of its floating and wandering cells. The only indication that I get as to their use points to a possible nutritive function. The enlarged terminal portion of the canal of the sensory club almost invariably contains a number of the small-sized floating cells. These have a vacuolated, half disintegrated appearance, with the nucleus always compact and brightly staining. Now, examination of the high columnar cells that line the enlargement of the canal shows the presence in the cells of bodies of exactly the same appearance as those in the lumen. In one case a floating cell was found just at the end of an epithelial cell, to all appearance half ingested. The identity of the bodies inside the cells and those in the lumen is shown very clearly in some sections of material fixed in formalin, which preserves nuclei, cell walls and general outlines well enough, but does not retain the cytoplasm, and hence is useless for most purposes of histology. In the endodermal cells of the terminal enlargement thus preserved are found all the more distinctly the bright, compact, degenerated nuclei of the ingested cells, while in the lumen are seen other bright, compact nuclei with the poorly preserved remains of cell substances around them. In addition to the evidence from the appearance of the floating cells themselves and their ingestion by the endodermal cells, a little collateral evidence may perhaps be brought in from the Tripedalia about to be described. From the ovaries in this form are detached masses of cells ([Fig. 71]) which float free in the stomach pockets among the developing embryos, and to judge from the vacuolation that appears, are used up in their favor. These cell masses are described more fully in the part on Tripedalia.
B: Tripedalia Cystophora.
a. Habitat.
The species upon which the new family was founded was obtained in great abundance in one locality in Kingston Harbor in the summer of 1896. The environment was even more unlike that in which Cubomedusæ have been found heretofore than in the case of Charybdea Xaymacana. On the west side of the Harbor there is a part more or less cut off from the main body of water, and so from the ocean, by a peninsula. This sheltered bay is dotted with small mangrove islands which toward the head of the bay become so numerous as virtually to convert it into a mangrove swamp. The water is shallow and discolored with organic matter, showing that the tide does not exercise much influence here, and the bottom is for the most part a black mud, deep enough to make wading very uncomfortable but not impossible near shore. The islands rise but slightly above the level of the waters, and the thick vegetation that covers them, for the most part mangroves, grows out into the water on all sides, forming a fringe of overhanging boughs. It was here in the shelter of the boughs, among the roots and half-submerged stems of the mangroves, that the small Cubomedusa was found to thrive. It could be obtained in great abundance almost any day, and of all sizes from the largest adults with stomach pockets filled with eggs or embryos down to small specimens only about two millimeters in diameter. In but one other place was Tripedalia found, and that was a similar region of half landlocked water skirted with mangroves, situated near Port Royal, across the harbor from the locality just mentioned. It would be hard to find places in which the conditions of life were more strikingly different from those of the pure deep sea in which the Cubomedusæ have been generally found before. The slight brownish yellow pigment made the small medusæ a little difficult to see in the discolored water, but like the pellucid Charybdea in the clear water of the harbor, their active movements gave away their presence. The swimming was very vigorous and was effected by quick, strong pulsations (as many as 120 per minute were counted), very different from the slow, rhythmic contractions of the Discomedusan Cassiopea which was found in the same region over by Port Royal. Whether or not the animal made intentional efforts to escape capture could not be decided satisfactorily, but certain it was that they did escape often enough by swimming quickly below the surface of the semi-opaque water.
Tripedalia endured captivity much more hardily than the Charybdea, and would live in aquaria happily enough for a number of days—no attempt was made to see how long. Specimens with their stomach pockets filled with ripe spermatozoa, or with young at any stage from egg to planula, were taken in plenty from the latter part of June to the latter part of July. In each female the young were all at the same stage. The embryos were thrown out in the aquaria as free-swimming planulæ, which settled down on the bottom and sides of the glass in a day or two, and quickly developed into small hydras with mouth and typically with four tentacles (and four tænioles, W. K. B.), though three and five were by no means uncommon. In this condition they lived for three weeks without essential change, and they were still giving no promise of further development when the laboratory broke up and the jars had to be emptied.