MATURATION 



it has been shown that the number of chromosomes in theoogoniaiseven, 

 the number in the spermatogonia odd. An exact halving of the sperma- 

 togonial number of chromosomes can not occur in such cases (p. 23). 



\ 



K 



FIG. II. Reduction of chromosomes in the spermatogenesis of Ascaris megalocephala 

 bivalens (Brauer, Wilson). X about I loo. A-G, successive stages in the division of the pri- 

 mary spermatocyte'. The original reticulum undergoes a very early division of the chromatin 

 granules which then form a quadruply split spireme (5, in profile). This becomes shorter (C, 

 in profile), and then breaks in two to form two tetrads (D, in profile), (E, on end). F, G, H, first 

 division to form two secondary spermatocytes, each receiving two dyads. /, secondary sperma- 

 tocyte. J, K, the same dividing. L, two resulting spermatids, each containing two monads 

 or chromosomes. 



Oogenesis. During oogenesis, the ova undergo a similar process of 

 maturation. Two cell divisions take place, but with this difference: the 

 cleavage is unequal, and, instead of four cells of equal size resulting, there 

 are formed one large ripe ovum, or oocyte, and three rudimentary or abor- 

 tive ova known as polar bodies, or polocytes. The number of chromosomes 



