SEX INHERITANCE 



99 



But another difference is necessary to determine 

 whether an egg of the latter individual develops into 

 a male or into a female, namely, the entrance of a 

 spermatozoon into the egg before it has completed 

 its growth. 



FIG. 34. Diagram to illustrate the life cycle of Phylloxera carysecaulis. 



In the phylloxerans of the hickories the fertilized 

 egg gives rise to a female called the stem mother 

 (Fig. 34). She emerges from the egg in the early 

 spring and attaches herself by means of her proboscis 

 to a leaf, causing it to produce a gall that envelops 

 her. Within the gall she lays her eggs. These 

 hatch, and produce the winged or migrant generation 



