244 T. H. Morgan 
SEX DETERMINATION IN PHYLLOXERA FALLAX 
This species is found abundantly inthe vicinity of New York on 
young hickories, or on the lower leaves of older trees. When well 
infected the leaves are covered thickly with the conical galls. 
There is some question as to the identification of the species owing 
to differences of observation as to its life cycle. A discussion of 
this matter is relegated to another section. Here it will suffice to 
say that in many galls the winged generation is replaced by wing- 
less individuals (Fig. XVIII, 4), and these lay the male and female 
eggs within the gall itself, where they hatch. Owing to this 
unusual habit it is possible to collect quantities of the sexual eggs 
and embryos. The formation of the spermatozoon takes place 
within the male embryo before it hatches. Abundant material 
for the study of spermatogenesis is therefore readily obtained. 
The stem-mother begins to deposit her eggs, one at a time, before. 
the gall reaches full size. The number of eggs is variable, and 
since the first may hatch, and grow up into an adult which begins 
to lay, before the stem-mother has completed her series, there may 
be some overlapping of the two sets of eggs. “The number of eggs 
@m@Q wv 
Fig. I P. fallax. A, Equatorial plate of a polar spindle of egg of stem-mother; B, side view of 
polar spindle; C, chromosomes of somatic cell of embryo from egg of stem-mother; D-E, two sections 
of nucleus of same; F, another nucleus of same. 
