576 SIDNEY I. KORNHAUSER 
s. 8). The sternum of the ninth segment, instead of being a 
single heart-shaped plate, is represented by two minute sclerites, 
each placed laterad against the clasper of its corresponding side 
and about equidistant from the ends of this organ. It would be 
difficult to explain these changes in infected males as being 
due to mechanical necessity caused by alterations of the gona- 
pophyses, and they can only be understood, I believe, in looking 
at them as a partial assumption of female characteristics. 
The sterna of parasitized females show the following changes: 
that of the seventh segment bears merely a notch in the median 
plane running cephalad from its caudal border; that of the eighth 
remains a single sclerite, being not quite bisected by the gona- 
pophyses (fig. 31, s.7, s.8) which are greatly shortened by the 
action of the parasites. The ninth segment presents the sternum 
in two sclerites, retaining their original position and articula- 
tions, but being somewhat larger than normal and less well 
chitinized. 
A distinct sexual difference is found in the tergum and pleura 
of the ninth abdominal segment. In the male (fig. 24, t. 9, p. 9) 
the tergum and pleura of this segment are separate sclerites 
which are united by a thin, pliable, chitinous membrane. The 
pleuron is almost semicircular and projects caudad beyond the 
tergum. In the female (fig. 28, ¢ 9, p. 9) these sclerites are 
much larger and quite different in form from those of the male. 
They are fused into one, the suture on each side being visible 
as a curved line passing from the anal tube to the lower border 
of the eighth tergum. The integument on each side of this 
suture is of a distinct character; the dorsal portion being similar 
to that of the other terga, whereas the ventral portion is beset 
with long hairs. The pleuron, unlike the semicircular sclerite 
of the male, is drawn into a long plate, extending almost the 
entire length of the external genitalia (fig. 29, p. 9). 
In parasitized males (figs. 26 and 27, t. 9, p. 9) the tergum and 
pleura fuse as in the female. Moreover, both plates increase in 
length, the pleura lose their semicircular form and fail to pro- 
ject caudad beyond the tergum. Thus all the male characteris- 
tics are lost and an approach to the female condition takes place. 
