Parasites 



;o9 



instance lays her eggs on the hairs of a horse's body ; 

 through licking the part the horse takes these eggs 

 into the mouth and swallows them. The grubs are 

 hatched and feed on the lining of the stomach ; being 

 at length cast out with the dung, they bury themselves 

 in the earth and pupate. These insects, and others 

 with similar habits, like the Ichneumon-flies, show the 



Fig. 167. — Horse Bot-fly (Gastrophitus equi, Fb.). a. egg on hair, magnified 

 (/'. natural size) ; c. young larva, magnified ; ci. more highly magnified ; e. 

 mouth-hooks ; _f. spines, still more magnified ; g. full-grown larva, twice 

 natural size; k. female, natural size. From Osborn, Bull. 5 (n.s.), U.S. 

 Dept. Agr., Div. Ent. 



degeneration due to parasitism only in the larval stage. 

 The imago is as perfectly developed as the average 

 insect of its order, a very complete separation between 

 the larval and imaginal stages being strongly brought 

 out in such cases. In the Stylopidae (p. 224) the female 

 who spends the whole of her life within the body of 

 a Bee retains always her maggot-like form, while the 



