SEX INHERITANCE 115 
The testes are destroyed, as a rule, by the parasite, 
and this, no doubt, has given rise to the view that 
the changes in the secondary sexual characters are 
due to the removal of the testes—a view all the 
more plausible since such effects were well known 
in the mammals and birds. But Giard did not 
commit himself wholly to such a view. He appears 
to have thought that the influence of the parasite 
might equally well be due to direct action on the 
crab. The more general view, that the action is 
through the loss of the gonads, has been challenged 
by Geoffrey Smith. His view may appear to be 
the more probable interpretation, but as yet it has 
not sufficient experimental verification. 
Kornhauser has recently discovered in one of 
the bugs (Fig. 36 F) a critical case that shows that 
a similar change in them is not due to the de- 
struction of the gonad, but directly to some kind 
of influence on the tissues of the host. The nymphs 
of the tree-hopper Thelia bimaculata are parasitized 
by a hymenopter, Aphelopus theliz. The egg 
deposited in the nymph produces a chain of young 
(polyembryony). The parasites in the male 
(Fig. 36, F, 1) cause it to develop certain characters, 
such as markings and some structural features, of 
the female (Fig. 36, F, 3-4). Usually the testes are 
destroyed; but in one case a testis was left and 
developed spermatozoa; nevertheless the nymph 
showed certain female characters. It is evident, 
therefore, that the change may take place inde- 
pendently of the gonads, and this is to be expected 
