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 thelise. 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 



