HISTOLOGY AND DEVELOPMENT OF MYRIOTHELA PHRTGIA. 509 



this is seen to be due to the presence of numberless minute 

 vacuoles. Each cell has embedded in its substance a hyaline 

 mass of uniform texture (fig. 2), which at first is deeply 

 placed in the cell, but as growth proceeds it is pushed to one 

 side (fig. 5 b), and eventually forms one of the curious rhabdite- 

 like nematocysts which stain so deeply with hsematoxylin and 

 osmic acid. The first formed amorphous hyaline masses, 

 however, stain only lightly with osmic acid, and, whatever the 

 chemical change may be which alters so profoundly their 

 behaviour towards that reagent, it does not occur until a 

 relatively late period in their development. I am not at all 

 certain that the hyaline masses found in these cells are, in 

 every case, early stages in the development of nematocysts. 

 For many reasons I am inclined to think that they may some- 

 times be of the nature of reserve nutritive material. My 

 researches on this point are, however, incomplete, and I will 

 merely content myself here with noting the fact that the very 

 earliest change in that part of the ectoderm where a gono- 

 phore is about to be developed, is amongst other things a local 

 accumulation of the large cells bearing hyaline masses, some- 

 times one, sometimes two (fig. 8), while at the same time there 

 is a total disappearance of nematocysts from that area. 



The deepest layer of the ectoderm of the gonophore-bearing 

 region is the most remarkable. It consists for the most part 

 of small rounded cells (fig. 6), either scattered about fairly 

 evenly, or, and more frequently, gathered into smaller or 

 larger clusters. If one of these clusters be examined with a 

 high power, the cells composing it are seen to present con- 

 siderable differences in size, varying from 8 /^ to 12 /u in 

 diameter. In most of the clusters, and more especially if the 

 blastostyle under examination be one which has scarcely 

 commenced to produce gonophores, few or many of the cells 

 will be found with two small nuclei, and the cluster will 

 betray other evidence of the active proliferation of its consti- 

 tuents (fig. 2). 



In those cells with a single nucleus, that nucleus is uniformly 

 of about 4 )Lt in diameter, and, like the nuclei generally, is 



