176 



HEREDITY AND SEX 



we may suppose that one sex chromosome is present 

 in the male or at least one differential factor for sex, 

 and that it is present in all the functional spermato- 

 zoa. The female will then have two such chromo- 

 somes and come under the general scheme for insects. 





':i/^- 





:fe 





c -% 



D -^ 



@ 



% 



8^ 



■8^ 







\<6<$ 



<?i6 



16 + 16 = 32. 



Fig. 90. — Oogenesis and spermatogenesis in bee. Four upper figures, 

 A-D, show formation of first (A), and second {B) polar bodies. Only inner 

 group of chromosomes remains (C) to form egg nucleus. Entrance of sperm 

 nucleus in D. E shows scheme of these two divisions involving eight double 

 (82) chromosomes. F, first and second spermatocyte divisions, the first, 

 a, b, abortive, leading to pinching off of a small cell without a nucleus, the 

 second, c, c, leading to formation of a large (functional) and an abortive 

 cell (above). 



In the gall fly, Neuroterus lenticularis, partheno- 

 genetic females appear early in the spring. Their eggs 

 produce females and males — the second generation. 

 The fertilized eggs of these females give rise the follow- 

 ing year to the spring parthenogenetic females. Don- 

 caster has found that each parthenogenetic female 



