SEXUAL CHARACTERISTICS OF THELIA 573 
emerging, distends even the enlarged abdomen to its full capac- 
ity. Moreover, the larvae would be unable to bore through 
normally chitinized sterna, so these plates are thin and trans- 
lucent in all parasitized individuals. 
The abdomens of parasitized females (figs. 30 and 31) remain 
in cross-section and size similar to those of normal females. A 
loss of pigment is seen in all the sclerites and the sterna remain 
thin and delicate as in parasitized males to permit the escape 
of the larvae. 
Turning now to a consideration of the details of the abdominal 
integument, we note two distinct sexual differences. The ab- 
dominal sclerites of the second to eighth segments, inclusive, 
possess long, scattered, chitinous hairs directed caudad, and in 
addition to these there are minute hairs forming very distinct 
patterns (figs. 32 to 35). These minute hairs are very differently 
arranged in the two sexes. Figures 32 to 35 are camera-lucida 
drawings representing a corresponding region of the sixth ab- 
dominal tergum of typical individuals. Figure 32 represents the 
arrangement found in normal males, fairly straight and com- 
pact rows running laterad and ventrad. The pattern on the 
female terga is strikingly different (fig. 34). The spines here 
form a network, made up roughly of rows of half-circles arranged 
alternately in such a way that the ends of the half-circles of one 
row touch the apexes of those in the row more anterior. 
In parasitized males (fig. 33) there is a complete loss of the 
characteristic arrangement of these spines and almost a com- 
plete assumption of the female pattern. The only difference 
to be noted is that the ends of the ares are not so well formed, 
usually lacking a few spines to complete the articulation with 
the row in front. This change of pattern is one of the clearest 
qualitative sexual changes in the abdomen of parasitized males 
and cannot be ascribed to anything except the assumption of 
a female characteristic. Parasitized females are similar to nor- 
mal females in the above-described characteristic (fig. 35). 
Short spines or hairs are also present on the sterna. In the 
male these are arranged in rows running in straight lines across 
the sterna from pleuron to pleuron. Camera-lucida drawings 
