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.