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. 



^4f^&3ce^uZ' cmy^eucaiiAd 



Sii^n- 7?MAe^ 



^.Jti^'t.ai/rU:. \/;yiz^dM£^A. 



^.Mi^'umX. )iyx<r(J.ucvt/ 



W 



<? 



Fig. 34. — Diagram to illustrate the life cycle of Phylloxera caryaecaulis. 



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 



