56 



CYTOLOGY 



CHAP. 



Another difference between gametogenesis in the male and female 

 has already been alluded ib, namely, the fact that in the female each 

 primary oocyte gives rise to only one functional gamete and three (or 

 two, if the first polar body does not divide) minute and functionless cells 

 (polar bodies) instead of to four functional gametes as in the male. This 

 is also obviously correlated with the necessity for the female gamete to 







D 



,^- 





*•■ 



■A 



^r* 



'^ ^ 







4 





;; 



ir. 



t'4'* • A 



Fig. 21. 



Early stages of oogenesis in the cat. (After von Winiwater and Sainmont, A .B., 1909.) A, young oocyte I., 

 chromatin mostly very finely divided ; B, C, development of leptotene stage ; D, zygotene ; E, pachytene ; 

 F, diplotene stages ; G, H, development of " germinal vesicle " stage. 



be very large and richly provided with reserve food material ; the 

 achievement of this is materially assisted by the concentration of prac- 

 tically the whole of the reserve material into one macrogamete, instead 

 of its partition among four. 



The correspondence between the mature egg with its polar bodies 

 and the four spermatids derived from one spermatocyte is of course only 

 complete in those cases where the first polar body divides into two, giving 



