OF THE ACALEPH^ OF NORTH AMERICA. 261 



such a State of dilatation, the mouth is almost square, and nearly as wide as the main 

 cavity, the lips being more or less sinuous. (Fig. 21, a.) In this condition of utmost dila- 

 tation, the continuity of the transparent mass of the lips with the base of the tentacles, 6, 

 is very obvious. The peduncle of the tentacles itself appears then simply as a prolonga- 

 tion of the mouth, protruded in the form of a branching margin. Here, the analogy 

 of the mouth with that of the common Medusae, such as Aurelia or Cyanea, is very 

 obvious, the only difiTerencc being, that the branching fringes are not so membranous, 

 but rather dendroid. 



The tentacles of the mouth, (Plate II. Fig. 18, c, c, d, d ; Fig. 21, b, c, c,c ; Fig. 23, 

 d, d,e, e, e; Fig. 25, 26,) like the lips, consist of a transparent cellular tissue, composed 

 of two layers of different cells. The inner layer, which forms the main stem and the 

 centre of the branches, consists of larger polygonal cells, (Fig. 25, 26, h, b, b,) while the 

 outer layer consists of much smaller stinging cells, (Fig. 25, 26, c, c, c,) provided with an 

 inner arrow-head (Fig. 27), like all nettling cells. Around the top of the branches of the 

 tentacles, these latter cells are arranged in bunches, in such a manner as to give each ter- 

 mination the appearance of a sucker. But even when employing the highest magnifying 

 power, I could discover no trace of an opening, but only the stinging cells in their 

 regular arrangement. That these tentacles cannot be organs of suction is plainly shown 

 by the fact, that their branches are not hollow, but consist of continuous cells. Their 

 function, as indicated by their structure, can only be that of retaining the prey. The 

 number of terminal ramifications in each bunch of tentacles is about one hundred, each 

 tentacle dividing first into two branches, which are somewhat unequal, and then subdivid- 

 ing dichotomously, but also somewhat irregularly ; for each of the bunches of the second 

 order is subdivided so far as to contain, one about twenty, and the other about thirty ter- 

 minal branches; amounting together to about one hundred terminal points in each ten- 

 tacle, and making, therefore, about four hundred of these branches around the mouth. 

 Each of the tips is surrounded by about a dozen stinging cells, varying in number accord- 

 ing to the size of the branches, being more numerous in the larger branches and fewer in 

 the smaller ones, and more numerous in old specimens than in younger ones. When fully 

 open, as described above, the mouth allows a sight into the centre of the digestive cavity, 

 which appears as an undulating surface, with honeycomb-like irregular depressions, (Plate 

 II. Fig. 21, e, e, e,) lined with an epithelium of a dark-brown color. Whether the deeper 

 brown cells under this epithelium are to be considered as hepatic cells, and whether 

 these little depressions are secreting cavities, I am unable to decide; but I should incline 

 to suppose that there are active finictions going on in these tissues, and that the differ- 

 ent layers of these cells do not perform the same functions, as the cavity contains always 



SQ 



