SEXUAL CHARACTERISTICS OF THELIA 627 
so that this organ could no longer be used in distinguishing hip- 
pocastani from certain other species. 
The color reversal in Thelia bimaculata was very complete in 
many parasitized males. If we examine various examples of the 
tribe Telamonini, to which Thelia belongs, we find that the 
coloration of the male is not often strikingly different from that 
of the female. In Thelia bimaculata we have an exceptional 
and extreme case of dimorphism in coloration. Thus in Thelia 
uhlert the nearest relative both sexes are of a reddish-brown 
color. Microscopical examination shows that a faintly out- 
lined lateral area on the pronotum corresponding to the vitta of 
bimaculata exists and that the melanic pigment of the pronotum 
is chiefly restricted to the punctures. No sexual difference 
either in the pigment or in the pattern on the pronotum or face 
could be found. The coloration certainly resembles that found 
in the female of bimaculata much more than the male, and I 
believe we are to look upon Thelia uhleri as representing a more 
ancestral type. There are several reasons for this. The gona- 
pophyses are quite similar in form to those of other genera of 
the Telamonini, as indicated by the bulbous oedagus and pointed 
ovipositor. Also the arrangement of the spines on the abdom- 
inal terga shows a greater similarity in the patterns of the sexes 
than was found in Thelia bimaculata. The rows in the male 
are not so straight and close together and the characteristic 
network arrangement of the female may also be found over 
parts of the male terga. Thus I believe that the coloration and 
arrangement of the abdominal spines in the male of Thelia 
bimaculata represent recent changes and that the female char- 
acteristics represent the more ancient and less modified con- 
dition, ‘These recent sexual characteristics of the male must 
have arisen through genetic changes modifying characteristics 
once common to both sexes. The genes for these characteristics 
of the male find their expression in the final ontogenetic step in 
the presence of one x-chromosome, and they probably depend 
upon all the changes in development which preceded them. Is 
it not likely that the internal upset caused by the parasites 
interferes with the normal expression of these male genes? 
JOURNAL OF MORPHOLOGY, VOL, $2, NO. 3 
