F. S. CONANT ON THE CUBOMEDUS^. 45 



the subumbrella, and I am inclined to ascribe to them also the import- 

 ance of special ganglia controlling the musculature of the frenula and 

 suspensoria. Certainly such ganglia would not be out of place. 



It has been mentioned that the greater prominence of the radial 

 nerve and the possession of special sensory organs in the proboscis were 

 the only points of difference I had noted between the nervous systems of 

 Charybdea and Tripedalia. These sensory organs remain to be described. 

 They are simple ciliated cysts containing a concretionary mass, and are 

 situated in the gelatine of the proboscis, irregularly disposed of at any 

 level, from the lips to the beginning of the stomach, and in any radius. 

 In one series of the adult animal fifteen were counted, of which seven 

 were situated about interradially, four perradially, two ad radially and 

 two subradially. In another, twenty-one were counted, twelve in the 

 perradii and nine situated between the sub- and perradii. The one 

 shown in Fig. 24 is in the perradial position, often seen. In the sections of 

 the very young Tripedalia in which the vascular lamella had not reached 

 the adult condition the sensory organs of the proboscis were not found, 

 although the sensory clubs showed practically no difference from the 

 adult. Their structure is very simple merely a round or oval sac lined 

 with ciliated cells which bear up and keep in constant motion an irreg- 

 ular coarsely granular concretion. Fig. 53 is a sketch made in Jamaica 

 from the living specimen. Sections were somewhat disappointing in 

 that they added but little. Fig. 55 was drawn to show that now and 

 then a mucous cell (me) is found among the other cells of the sensory 

 epithelium. An irregular-shaped mass (re) was always found inside the 

 cysts as the organic remains of the concretion. It gave no trace of 

 cellular structure and offered no evidence whether the concretion was 

 the product of one or few or of all the cells of the cyst. The latter would 

 be unique among the medusae. Even if the otocyst is the result of the 

 activity of only one or a few cells, it is, so far as I know, the only case 

 known for the jelly-fish of a free, unsuspended concretion. 



As to whether the cysts are of ectodermal or endodermal origin 

 could not be determined, but there was some evidence in favor of the 

 latter. Fig. 56 is a drawing of one seen in optical section in a whole 

 mount of part of a proboscis, and shows a definite connection with the 

 endoderm of the proboscis. This was the only case when such connec- 

 tion was satisfactorily established, but in sections it was not uncommon 

 to find what seemed to be the remains of the broken stalk, as in Fig. 54 

 (rs ?). No connection could be traced between the cysts and any other 



