HISTOLOGY AND DEVELOPMENT OF MYRIOTHELA PHRYGIA. 511 



concerned in the manufacture of nematocysts (fig. 4). In 

 some sections scanty patches of small cells similar to those 

 described above may be seen, but they are now the exception 

 and not the rule. On the other hand, over considerable 

 regions the ectoderm may be even more decrepit than that de- 

 scribed above, for even the columnar cell layer may be imper- 

 fect, while the basal cells are represented largely by irregular 

 spaces. On the other hand, the muscular layer and supporting 

 lamella are proportionately better developed. Measured from 

 the external surface of the cuticle to the external surface of 

 the supporting lamella the ectoderm at this period is from 30 

 to 35 fx in thickness. 



We thus see that as the season advances and the reproductive 

 period comes to a close the ectoderm of the gonophore-bearing 

 region becomes more and more exhausted of those small cells 

 which are such a characteristic feature of it in the spring, and 

 I think there can be little doubt that their disappearance is 

 connected with the active formation of gonophores during the 

 summer months. 



So far I have spoken of them merely as the small cells of the 

 proximal ectoderm. It is necessary to see whether these cells 

 ai'c all alike, or whether they may be divided into one or more 

 sets differing in their function and connections. In tracing 

 the process of formation of the nematocysts I have said that 

 they first appear as a rounded hyaline mass embedded in the 

 protoplasm of a cell which then lies in the deeper part of the 

 ectoderm. 



The smallest cells containing these masses may be only 10 ;x 

 in diameter ; but though they do not difi'er markedly from the 

 bulk of the small cells in point of size, they do differ in one 

 very important particular, namely, in the fact that they are 

 always connected by a delicate process with the nerve network 

 (fig. 5). 



On the other hand, we have in addition to these small cells 

 which are in connection with the nerve network, and so often 

 contain some trace of a developing nematocyst, other still 

 smaller rounded cells, which appear, even with the highest 



