54 GERM-CELL CYCLE IN ANIMALS 



becomes separated from the rest of the ovary and is 

 forced by the movements of the larva into some other 

 part of its body. Here it continues its growth and 

 development at the expense of the tissues of the 

 mother-larva. Not all of the oocytes (thirty-two 

 in each ovary) complete their development, since 

 ^usually only from five to seventeen young are 

 produced by a single mother-larva. Those oocytes 

 that do not perish pass through the stages described 

 in the following paragraphs. 



. Figure 13 represents the condition of an oocyte just 

 before the initiation of the maturation processes. 

 The nucleus, or germinal vesicle (g.v.), is eccentrically 

 placed and nearer the anterior than the posterior 

 end of the cell. The nurse chamber has greatly 

 decreased in volume. 



The contents of the oocyte are not homogeneous, 

 but several distinct regions can be distinguished. 

 Near the nurse chamber is a body of cytoplasm 

 evidently elaborated by the nurse cells, and at the 

 posterior end is an accumulation which we may call 

 the pole-plasm (pPl) and which is of particular 

 interest since it is intimately associated with the 

 formation of the primordial germ cell. 



The maturation division occurs soon after the 

 stage just described has been attained. The ger- 

 minal vesicle, which lies near the periphery of the 

 oocyte, breaks down, and the chromatin contained 

 within it becomes aggregated into about twenty 

 chromosomes. As a result of the maturation division 

 (Fig. 14) a polar body (p.b) and the female pronucleus 



