Mr. F. S. Conant on the Cubomeclusse. 39 



d. The vitreous body, over and above these " visual 

 fibres " and " pigment-streaks," is not a homogeneous secre- 

 tion, but is composed of prisms of gelatinous refracting sub- 

 stance, each with a denser central fibre. The size of the 

 cross- sections of these prisms corresponds with that of the 

 cross-sections of the mtijoritj of retinal cells. It is probable, 

 tlierefore^ tliat thej represent the outer ends of retinal cells. 



From the above it will be seen that I find in the vitreous 

 body two structures in addition to Schewiakoflf's visual pro- 

 cesses — namely, similar processes from the "pigment- 

 streaks," and the prisms that make up the mass of the body. 

 I am inclined to believe that the retina contains at any rate 

 two, and perhaps three, kinds of cells, but that these are 

 distinguishable only by that part of them which lies in the 

 vitreous body, and are not distinguishable in the retina as 

 two. alternating types, as figured by Schewiakoff". 



In another point also I am unable to agree with Schewia- 

 koff. In one region of the sensory club is found a mass of 

 peculiar large, closely packed, polygonal cells, which he affirms 

 to be ganglion-cells, as against Claus, who considers them 

 supporting cells. In my sections they show nothing what- 

 ever to suggest a resemblance to ganglion-cells. No processes 

 could be made out, and the body of the cell consisted of a 

 beautiful cytoplasmic reticulum with thickenings at the nodes 

 of the rather coarse meshes. 



The sensory organs in the proboscis of Tripedalia are simple 

 cysts of ciliated epithelium lying in the gelatine. The long 

 cilia support and keep in constant motion an otolith of ragged 

 outline, in which no trace of cellular structure was found. 

 This is the only case, so far as I know, of the occurrence 

 among the Medusas of a free unsuspended otolith in a ciliated 

 sac. 



D. — Development. 



Females of Tripedalia were found with stomach-pouches or 

 pockets filled with developing ova, so that I am able to offer 

 a few facts prehmmarily on the development of the Cubo- 

 medusEe. The mature eggs pass from the ovaries into the 

 stomach-pouches, and there develop up to the stage of free- 

 swimming planulas. In with them are found floating masses 

 of cells, showing here and there a nematocyst, whose struc- 

 ture points clearly to an origin from the ovary also. These 

 masses circulate about among the developing ova, and serve 

 for protection and apparently also for nutrition, since the cells 

 are found vacuolated in masses from individuals containino- 

 well-advanced embryos. All the eggs or embryos in one 



