SEXUAL CHARACTERISTICS OF THELIA 067 
known to cause the degeneration of wing muscles in certain 
Acridiidae (Kiinekel d’Herculais, 94), making volitation impos- 
sible, parasitized Thelia can both fly and jump quite as well as 
ordinary females. To move the enlarged wings and transport 
the increased bulk of the body certainly larger muscles are 
necessary. 
B. The head 
If we examine the sexual distinctions in the heads of Thelia 
we find differences of color, pattern, and size. The hypodermal 
pigment is similar to that of the pronotum in the respective 
sexes, being orange-yellow on the vertices and clypeus of the 
male and greenish-yellow in the female. ‘There is also a sexual 
difference in the distribution of the melanic pigment of the face 
(fig. 22.), which is not only darker brown in the male, but also 
more abundant and less scattered than in the female. On the 
vertex about each ocellus the male has a well-defined spot, and 
along the medium suture between the vertices there is a distinct 
line of brown pigment. From this vertical line there are two 
diverging arms bordering the upper edge of the clypeus and 
forming an inverted Y. The male clypeus has two distinct 
bands extending ventrad from the arms of this inverted Y. 
Along its lower angle and the borders of the genae it is deeply 
pigmented. In the female, the melanic pattern is less distinct, 
being present in smaller and more irregular patches. Especially 
is this noticeable on the lower border of the clypeus which is a 
mottled light brown in the female, deep solid brown in the male. 
Parasitized males not only lose the orange-yellow hypodermal 
pigment which is replaced by greenish-yellow pigment, but in 
fully altered specimens also exhibit the melanic pattern char- 
acteristic of the female head. These changes cannot be ascribed 
to the retention of juvenal characteristics, for the color, pattern, 
and structure of the integument of the nymphal head (fig. 22, ny.) 
differ greatly from those of the adult and resemble the nymphal 
integument of the thorax and abdomen as described on page 563. 
A comparison of head widths, measured at the level of the 
compound eyes, reveals the fact that parasitized males show an 
