G6 THE MEDUSAE. 



The gastro-vascular system is typical of the genus, the stomach being fiat, 

 the mouth surrounded by a simple circular lip, and usually widely opened. 

 The gastric pockets, which vary in breadth, are nearly square in outline. 

 The aboral gastric wall is evidently very delicate, for in all the specimens 

 it is more or less torn over the central regions of the pockets (PL 16, fig. 5). 

 When the wall is entirely torn away over the pockets, as is often the case in 

 battered specimens, it is seen that the convexity of the pockets is caused 

 by swellings or prominences of the aboral side of the gelatinous disc, com- 

 parable to the genital prominences which occur in the same region in the 

 Solmaridae (p. 86). There is no trace of either peronial or ring canals. 

 Neither is there any definite cell-strand which might be supposed to represent 

 a circular canal. Such a cell-strand has been described and figured by the 

 Hertwigs ('78) for S. albescens, but the only approach to such a structure 

 which I have been able to find in the present species is a slight crowding of 

 the endoderm cells (PI. 21, fig. 8). 



The sexual products are located on the gastric pockets chiefly near their 

 margins, never, so far as I have observed, occurring on other regions of the 

 gastric wall. In a mature female the gonads consist of a number of oval 

 swellings, lying as a rule in radial folds, each swelling inclosing a single very 

 large egg (PI. 21, fig. 7). Considering the very great size of the eggs (1 mm. 

 in length), and the thinness of the ectodermal layer which encloses them, it 

 seems probable that they are set free by the breaking down of the latter, 

 which would account for the fact that the gastric wall is so often torn in the 

 neighborhood where the gonads develop. In the male the sexual products 

 are developed more evenly over the surface of the pockets. Agassiz and 

 Mayer (: 02) described the gonads in this species as horseshoe-shaped and 

 lying in the interradii, i.e. between the tentacles; but from their figures 

 (: 02, pi. 5, figs. 23, 2^), it is evident that in their single specimen the entire 

 aboral LT.ist ri«r wall was torn away over the region of the pockets, and that 

 tin- structures they have described as gonads were, in reality, nothing more 

 than those portions of the wall which remain adhering in the regions of the 

 interradial septa which separate the pockets. This condition was seen in 

 several fragmentary specimens in the present collection. 



This species is entirely colorless. 



Solmissm mcwshalli is a surface form. 



The present captures, together with the ones recorded by Agassiz and 

 Mayer (:02) from the Marshall [slands, ami by Mayer (: 06, p. 1134) from 



