286 The Ohio Journal of Science [Vol. XVIII, No. 8, 



Marchal (1897) studied in detail the pathological conditions 

 that Trichacis remulus Walk, produced in its host Mayetiola 

 destructor, the Hessian fly. He observed that the Trichacis 

 larva is always in intimate connection with the nervous system 

 of the cecidomyid larva and he noted the remarkable cell 

 proliferations that are brought about by the parasite. Although 

 he did not find the early stages and therefore was unable to 

 state anything about their origin, he made some striking con- 

 clusions, saying that ' ' These groups of giant cells are evidently 

 destined to accumulate nutritive materials necessary for the 

 parasite. They are a kind of internal animal gall developed 

 by the presence of the Hymenopteron. " 



Keilin and Thompson (1915) noticed the peculiar mass of 

 hypertrophied tissue formed within Erythroneura hippocastani 

 parasitized by Aphelopus melaleiiciis and traced its origin to 

 the hypodermal cells which are stimulated to abnormal growth 

 by the presence of the parasite. The early stages of the dryinid 

 were found to be enclosed by this tissue similar to that in the 

 Trichacis larva, shutting the parasite off from the viscera of 

 the host. This cyst was noticed to be surrounded by a mem- 

 brane which persisted after the parasite larva had assumed the 

 curved position and had broken through to the exterior of the 

 host. They believe that the parasite draws its nourishment 

 from its host through the cyst membrane until the fifth stage 

 is reached, and that the tissue is not a phagocytic cyst. They 

 compare the cyst to the placenta in animals or to a vegetable 

 gall and term the parasitism " placentaire'' or " gallicole. " 



Kornhauser (1915-16) in studying the effects of Aphelopus 

 parasitism on Thelia bimaciilata observed marked changes in 

 the external characteristics of the sexes, especially in the size 

 and form of the male and a reduction of the external genitalia 

 of both sexes, stating that "the presence of parasites in the 

 male nymph brings about lower oxidation, storing of fat, 

 retarded rate of development, increased size; and with this 

 change in metabolism comes a change in some of the secondary 

 sexual characters. But changed metabolism is not powerful 

 enough to change the external genitalia, it merely reduces 

 them in size. " 



In studying the effects of the parasitism of Aphelopus 

 comesi on Erythroneura comes the writer was able to confirm 

 many of Keilin and Thompson's observations and to add a 

 number of interesting points. The early phases were not studied 



