DISEASES OF INSECTS. 219 



their length, emulate the giants amongst insects. The 

 former, unless appropriated to the eggs themselves, usu- 

 ally commit many eggs to a single larva, while the latter 

 are directed by their instinct to introduce into them only 

 one. Some of the former description are endowed with 

 the faculty of leaping \ The food of Ichneumons, and 

 indeed of other internal parasites, is chiefly the epiploon 

 or fat of the larva, but they never touch any vital organ ; 

 so that it continues to feed, and probably more voraci- 

 ously, grow, cast its skin, and often it changes to a chry- 

 salis, although at the same time inhabited by an army of 

 these little devourers. 



Ichneumons, as far as has been at present ascertained, 

 are parasitic upon othe.r insects chiefly in their three first 

 states, a solitary instance only having been observed of 

 their inhabiting an imago but from their first exclusion 

 as eggs from the ovary till their assumption of that state 

 they give them no rest. I shall therefore first treat of 

 those that infest the eggs ; next those appropriated to 

 larvae ; and lastly those that devour pupae. 



Vallisnieri appears to have been the first naturalist 

 who discovered that Ichneumons were appropriated to 

 the eggs of other insects. He observed one proceed 

 from those of the emperor-moth (Saturnia Spini] : find- 

 ing two holes in each egg, one larger than the other, he 

 conjectured that one was made when it entered, and the 

 other when it emerged. In this case the egg of the 

 Ichneumon must be fixed on the outside of the egg it 



a De Geer i. 608. Linne has made a mistake with regard to the 

 Ichneumon here alluded to, in calling De Geer's saltatorious Ichneu- 

 mon /. Muscarum, and referring for it to t. xxxii./. 19, 20 of that 

 author ; whereas the Ichneumon that preys upon the aphidivorous 

 flies does not jump, and is figured by De Geer 605. t. xxxiv./. 20 

 29. The jumping one feeds on the larva of a Coccinclla. 



