SEX INHERITANCE 101 



Morgan). When the male appears, one chromosome 

 less is found in his somatic cells, and, since in the 

 nearly related phylloxerans a similar reduction takes 

 place and has been seen (Morgan) to be due to the 

 extrusion into the polar body of whole chromosomes, 

 it is practically certain that in the aphids the loss 

 takes place in the same way. 



In the first spermatocyte division in the aphids 

 (Fig. 33 B, a-c), one cell gets the unpaired X 

 chromosome (the mate of the one lost in the polar 

 body when the male egg matured), and this cell 

 after another equational division (Fig. 33 B, e-f) 

 produces two functional spermatozoa. The cell 

 lacking the X degenerates. The sexual egg gives 

 off two polar bodies. It then contains the reduced 

 number of chromosomes including one X. Such 

 an egg fertilized by the functional X-bearing sperm 

 gives rise the following year to the stem-mother, 

 which becomes the progenitor of a new line of par- 

 thenogenetic females, etc. 



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^ tlie winged or migrant gener- 

 ation (Fig. 34). Ill one species, P. carysecauhs, all 

 the migrants in one gall are alike in that they 

 produce the same kind of egg, i.e., in some galls all 

 the migrants contain large eggs (that produce sexual 



