74 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



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 Cubomedusa? 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, Glaus, Conant 

 and Maas'- 2 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 Chary bdea, 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). Glaus describes these muscle- 

 fibers and mentions that Fr. Miiller 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. Glaus suggests that the muscles 

 are developed from the cnidoblasts. 



(b) The plain subectodermal muscle-fibers are of interest. In 



