EARLY DEVELOPMENT OF HYDRA. / 



in part, make up the primitive ova. In these cells begins the 

 coalescing process, which is attended by marked cytological 

 changes. The chromatin network retreats further from the 

 nucleolus (Fig. 2, PI. I., a), and finally assembles as a well- 

 defined coarse spireme (Fig. 2, PI. I., b). Coincidently with this 

 process, the nuclear membrane becomes less distinct and even 

 absent in places. Within the nucleolus of these large, and fre- 

 quently of even smaller cells, two or three minute vacuoles ap- 

 pear, and these may, in rare cases, number seven or eight. As 

 the nucleus enlarges these vacuoles become larger and finally 

 unite to form one which almost entirely fills the nucleolus ; the 

 chromatin filament becomes broken up into short strands ; the 

 nuclear membrane disappears entirely, and the nucleolus, fre- 

 quently filled with the single large vacuole, very often migrates 

 out of the chromatin strands (Fig. 5, PI. I.). Associated with 

 these processes is the disappearance of the cell-walls of those 

 cells concerned in the changes. They become more and more 

 indistinct and finally disappear entirely, or nearly so, as a result 

 of which the substance of the several cells concerned unites to 

 form a single mass (Fig. 4, PI. I.). The mass formed by the 

 fusion of these cells is the egg, in process of growth. It is 

 interesting to note that there are several metaplasmic bodies in 

 many of these cells as already described, but that now they are 

 even larger and more pronounced. 



The disappearance of the cell walls in the manner above de- 

 scribed sets free the nucleus or its parts in the cytoplasmic mass 

 of the ^^g. The coarse spireme of chromatin material becomes 

 broken up into short strands which become dispersed and dis- 

 appear entirely, though careful search in the cytoplasm of an &gg 

 will frequently reveal fragments whose presence therein is easily 

 explained by the above account of the processes which take place 

 (Fig. 9, PI. II.). 



Not all of the nuclei which contribute to the mass of the &^^ 

 undergo this fragmenting process. Some persist apparently 

 unchanged even for some time but their ultimate fate, save prob- 

 ably in the case of one, is in the formation of the so-called pseudo- 

 cells which is to be described hereafter. 



The &g^ mass now becomes distinctly vesicular, and imbedded 



