Nos. 622-623] THE SEXES IN THE APHID 



51 1 



also pointed out that the conclusion regarding the rela- 

 tion of the winged and wingless viviparous females to 

 each other that was drawn from Tables I and II is con- 

 firmed in Table III. 



Progressive Change in the Frequency of all the Forms in 

 Successive Generations 

 Confirmation of the conclusions drawn from the pre- 

 ceding experiments is found in several lines which were 

 designed to show the normal life cycle over a consider- 

 able period when each generation was derived from wing- 

 less parents. In addition, these lines show a progressive 

 change in frequency of both the winged and wingless 

 viviparous forms and of the sexes. Owing to this pro- 

 gressive change it was not possible to maintain uniform 

 parentage, since in the late generations there were no 

 apterous individuals from which to breed. The princi- 

 pal lines were obtained in the three following experi- 

 ments. 



