290 T. H. MORGAN 



result is the same whether the lagging bodies represent two X 

 chromosomes, or one X chromosome precociously split, for on either 

 view eight (half) autosomes and two whole chromosomes {X) pass 

 out of the egg, leaving eight half autosomes and two whole {X) 

 chromosomes within the egg. 



The polar bodies of three other male-producing eggs are also 

 shown in plate 1, figures h, i, j. These show one or two dark 

 staining granules outside of the nucleus of the polar body, which 

 I interpret as the remains of the lagging chromosome. In this 

 respect they behave in the same way as do the lagging chromo- 

 somes in P. caryaecaulis which also fail to enter the nucleus of 

 the polar body. A fourth drawing, figure k, represents a late 

 stage in polar body formation in which twelve chromosomes are 

 distinctly counted in the inner nucleus of the polar spindle. The 

 outer nucleus is only partly present in this section, and the rest 

 of it could not be found in the neighboring sections. This egg 

 must have been a female-producing egg in which there is no 

 lagging chromosome, and in which there are twelve chromosomes 

 at the inner pole. 



Bringing these facts into relation to those already made out, 

 we can construct the chromosome cycle of P. fallax, and with 

 this as a clue make clear the similar cycle of P. caryaecaulis. 



THE CHROMOSOME CYCLE OF PHYLLOXERA FALLAX 



The main phases in the cj^cle are as follows: 



1. There is a single kind of stem-mother in this species whose 

 eggs contain twelve chromosomes that divide when the single 

 polar body is given off, so that twelve chromosomes pass out 

 and twelve remain in the egg (plate 1 , a to /) . 



2. These eggs develop into wingless females that produce 

 large and small eggs, but whether the same female produces large 

 and small eggs could not be determined. Both kinds of eggs 

 are found within the same gall, and therefore come from daugh- 

 ters of one original stem-mother, 



3. The large egg — the so-called female-producing egg — gives 

 off one polar body, all the chromosomes dividing at this time 

 (plate 1, A). This egg develops into the sexual female. The 



