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- 
Stern. Nether 
3 
Migrant. [producer 
9 
; K 
cy 
Fie. 384.—Diagram to illustrate the life cycle of Phylloxera caryxcaulis . 
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 shown in Fig. 35. In P. caryecaulis there 
are eight chromosomes, including four sex chromo- 
