Sex Determination in Phylloxerans and Aphids 279 
the male in twoimportant respects; first, the dwarf individuals have 
a very long proboscis which in this species is absent in the male; 
second, there are no testes within the abdomen as in the males, 
where they form a relatively enormous mass. Otherwise the 
dwarfs are so similar in external form to the sexual males that their 
true nature was uncertain until they were studied in serial sections. 
These showed the absence of the testes and the presence of rudi- 
mentary ovaries and ducts resembling those of immature partheno- 
genetic females. There was nothing to indicate that the dwarfs 
could become sexual females. In fact the latter contain each an . 
enormous egg when they hatch. 
The dwarfs can at once be distinguished from the young of the 
same generation by the length of the proboscis. In the dwarfs the 
proboscis is as long as the body, while in the young it is not more 
than two-thirds as long. The presence of the well-developed 
proboscis might lead one to infer an exceptional ability for pro- 
longed life, and this might readily suggest that these minute 
individuals are predestined to short circuit the life-cycle by remain- 
ing on the tree to produce the sexual forms of the following year. 
While I cannot positively deny to them such an existence, the facts 
that I have indicate on the contrary that these dwarfs are des- 
tined to a brief existence, and die without progeny. 
Inthe following table, I, (June 4) I give the results of an examina- 
tion of the contents of 166 galls. In the first column is given the 
number of the gall; in the second, the size of the gall; in the third, 
the total number of individuals; in the fourth, the number of large 
wingless or winged individuals. For very young stages it is not 
easy to detect the wings, but for older stages the presence of rudi- 
mentary (or of complete) wings is readily seen. When the wings 
are spread, i. e., when the insect is an imago, [ have underscored 
the figures indicating the number of individuals. The other 
columns include the number of eggs and the number of dwarfs or 
supernumerary females. 
