102 



SEX INHERITANCE 



females), while in other galls all of the migrants 

 contain smaller eggs (that develop into males). 



The sexual female lays one large egg, the winter 

 egg, from which the stem-mother emerges the fol- 

 lowing spring. The males give rise only to female- 



c^/y^^x^yui^ ca^fa£cai^A>> 



JTe-fTi, mciMfJi. 



€ 





Fig. 34. — Diagnun to illu.strate the life cycle of Phylloxera carya>cauli.-» . 



producing sperm, each spermatozoon containing 

 two sex chromosomes. The other class of sperm 

 degenerates. Hence we can understand why it is 

 that all fertilized eggs produce females only. 



The chromosomal cycle undergoes the series of 

 changes shoAvn in Fig. 35. In P. carj^secaulis there 

 are eight chromosomes, including four sex chromo- 



