100 



SEX INHERITANCE 



develop further. Since one maturation division of 

 the chromosomes, presumably equational, takes 

 place, the functional sperm has the haploid number 

 of chromosomes. All the sperm are alike, and any 

 egg that is fertilized gives rise to a female, which is 

 diploid. 



In some of the aphids there may be a long suc- 

 cession of parthenogenetic females, whose continu- 



a 



Fig. 33B.— Spermatogenesis of the bear-berry aphid, a, b, c, first sper- 

 matocyte division, with lagging chromosome. (/, interkinesis stage. e,f, g, 

 second spermatocyte division of functional cell. 



ance has been shown to depend on environmental 

 conditions. At the end of the series males and 

 sexual females appear. 



The parthenogenetic females have the diploid 

 number of chromosomes (Stevens, von Baer, 



