GERM CELLS AND THEIR FORMATION 



119 



may be related to each ovum. The nurse cells in many or 

 even in most cases, are cells which were potentially germ 

 cells, but which have lost their germinal potentiality and 



FIG. 65. Sections through ovarian ova and nurse cells in the Annulate, 

 Ophryotrocha. From Wilson, "Cell," after Korschelt. A. Young stage, the 

 nurse cell, n, larger than the egg. B. Growth of the ovum, o. C. Late stage, 

 the nurse cell degenerating. 



become wholly nutritive, contributing to the formation of 

 the true germ cell, degenerating and disappearing completely 

 after the ovum is grown and has left the ovary. In the other 



A B 



FIG. 66. Sections through ovarian eggs and their follicles in, A, young magpie; 

 B, newly born child. From Wilson, "Cell," after Mertens. 



cases, which are commonest among the Vertebrates, almost uni- 

 versal among them in fact, the ovarian cells adjoining the ovum 

 themselves potentially germ cells originally, form around the 

 ovum a definite layer termed the follicle (Fig. 66). The follicle 



