606 SIDNEY I. KORNHAUSER 
insects. One might offer a simple explanation, that the ab- 
domen increases because the parasites make this a mechanical 
necessity and this change induces an adaptive increase in other 
parts of the body: the wings must be larger to carry the increased 
bulk of the abdomen through the air; the thorax must be larger 
to contain wing muscles of increased strength. But there are 
serious obstacles to such an explanation. Very often the para- 
sites do not distend the abdomen of the host at its final molt 
and still the sclerites are so enlarged that later these larvae which 
increase tremendously can be accommodated. The influence 
is, therefore, not by mechanical stimulus. In many cases of 
parasitism in insects it has been observed that, although the 
abdomen may be greatly enlarged, the other parts of the body 
either remain normal in size or are even reduced. Wheeler (10) 
cites several cases in which ants with enlarged abdomens con- 
taining mematodes possess heads of normal size and wings greatly 
reduced. Perez (’86) states that in stylopized Andraenae the 
heads of the bees in both sexes are smaller than normal. It is, . 
therefore, rather remarkable that male Thelia increase in all 
parts of the body when infested by Aphelopus. We would 
naturally expect that the drain upon the nutritive material of an 
immature host would result in a starved undersized adult. 
In Thelia, although the infected males are larger than normal, 
still, in this sex as well as among the females, the parasites induce 
certain changes due to their demands upon the host. The 
gonads which are not essential to the life of the host are the 
first tissues to suffer and the material which would go in to the 
formation of countless numbers of spermatozoa or be used in 
the growth of ova doubtlessly affords one of the chief sources of 
nutriment for the parasites. The chitin, too, is often thinner 
than in normal individuals, this being noted on the pronota of 
females as well as males. The punctures may be smaller and 
shallower and the amount of melanic pigment restricted to the 
depressions of the punctures. Lack of materials demanded by 
the growing larvae might explain the absence of yellow pigment 
in the vittae of parasitized males but it would not explain the 
assumption of the female pigmentation nor would it account for 
