Sex Determination in Phylloxerans and Aphids 29g 
On May 23 young galls, many not yet closed in, were found. 
Each contained one stem-mother and from 1 to 83 eggs. The 
number of eggs is almost directly proportional to the size of the 
gall. ‘Thus in small galls the number of eggs was 3, I, 4, 3, 3, 
6, 4. 5, 0, O, O, O, 4, 9, I, 0, 2,2, Somewhat larger galls contained 
II, 13, 16, 6, 6, 8, Medium-sized galls contained 14, 18, 39, 29, 
23> 35> 27> 33> 38> 30, 37> 21s 47» 32> 45+ 37» 36 295 15s 43s 39) 445 
27) 203,10; 23. Big-galls contained’ 25,. 30, 30, 54, 30,.47,.42, 67, 
62, 74, 31, 83, 36, 46,22. Inthe largest galls a few of the eggs had 
hatched. 
Several days later (June 4) a considerable advance had beenmade. 
The chief events may be here summarized. Many of the eggs laid 
by the stem-mother had hatched. She was still present, however, 
and continued to lay eggs. The young that first hatched had 
become either wingless or winged individuals, or both in the same 
gall. The relation of these two kinds of individuals to each other 
is interesting and will be referred to later. The most important 
fact brought out by a study of the galls of this date (166 galls in all) 
is that there is a sudden break in the series of offspring; the eggs 
first laid producing individuals that grow to full-sized winged or 
wingless individuals, while those laid later produce a different kind 
of individual that never grows larger and remains throughout life 
the same size as when first hatched. These individuals I have 
named the supernumerary or dwarf females. Equally interesting 
is the discovery, that in the larger galls as many as 46 eggs may 
produce the large individuals, and then the smaller series 
abruptly begins; while in the smallest galls only one to three or 
four or more large individuals are produced when the small 
series begins. ‘There seems to be here not a predetermined num- 
ber of large and dwarf females, but the conditions of life deter- 
mine when the one kind ceases to be produced and the other kind 
begins. The two types of individuals must, however, be predeter- 
mined by alternative possibilities possessed by each egg. 
The supernumerary or dwarf females differ from their large 
wingless sister-forms, and from the young of the latter in a num- 
ber of points (Fig. XVIII). .The shape of the body is entirely 
different and resembles that of the sexual male; but it differs from 
