THE OVUM. 



57 



creases, partly, it appears, by an addition of fresh ones, and partly 

 by division. Owing to the latter process the germinal cells 

 come to form small masses or nests. The following description 

 of the further changes of these cells in the female refers in the 

 first instance to Elasmobranchii, but holds good in most respects 

 for other types as well. 



It is convenient to distinguish two modes in which the primi- 

 tive germinal cells may become converted into permanent ova, 

 though the morphological difference between the two modes is 

 of no great importance. 



In the first mode the protoplasm of all the cells forming a 

 nest unites into a single mass containing the nuclei of the pre- 

 viously independent ova (fig. 19, nn}. The nuclei in the nest in- 

 crease in number, probably by division, and at the same time the 

 nest itself increases in size. The nuclei while increasing in 



FIG. 19. SECTION THROUGH PART OF THE GERMINAL EPITHELIUM OF THE OVARY 

 OF SCYLLIUM AT THE TIME WHEN THE PRIMITIVE GERMINAL CELLS ARE 

 HECOMING CONVERTED INTO OVA. 



. Nests formed of agglomerated germinal cells. The nuclei of these cells are 

 imbedded in undivided protoplasm, do. developing ova. o. ovum with follicle. 

 po. primitive germinal cell. dv. blood-vessels. 



number also undergo important changes. A segregation of their 

 contents takes place, and the granular part (nuclear substance) 

 forms a mass close to one side of the membrane of the nucleus, 

 while the remainder of the nucleus is filled with a clear fluid. 

 The whole nucleus at the same time increases somewhat in size. 

 The granular mass gradually assumes a stellate form, and finally 



