THE CANADIAN ENTOMOLOGIST 47 



fully developed and have become highly active. Hence the need 

 for special uterine development. So far as yet known no elongate 

 unpediceled eggs are ever deposited on hosts except by the Gastro- 

 philine Cobboldiine and Cuterebrine flies, whose eggs are provided 

 with a profuse viscid coating for attachment by their lateral or 

 latero-anal surfaces to the hairs of the host. In this connection 

 it also becomes evident that forms affecting a host to which the 

 fly can not gain access must possess a uterus in which to develop 

 active maggots that can search for and penetrate to such hosts. 



Some maggot-depositing flies, on the other hand, which have 

 what would seem the most perfect access to the host are most 

 careful to keep at a certain distance from the latter. Such are the 

 Hystriciidae or leaf-larvipositing forms which are greatly specialized 

 in their coloured maggots, long coiled strap-like uterus, consoli- 

 dated cephalopharyngeal skeleton and excessive macrochaetal 

 development. Their very divergent host-relations may be in 

 part due to certain of their hosts living in webbed nests and being 

 in the habit of spinning sundry silken threads both for enlarging 

 and changing their habitations and for marking their feeding 

 trails whereby they may retrace their way to the nest. Silken 

 webs are especially dangerous to forms of excessive macrochaetal 

 development; and it may be that there is seme connection between 

 this and the origin of this remarkable host-habit, with the con- 

 sequent coloration of the maggot. 



Even more consolidated than in the Hystriciidce is the cephalo- 

 pharyngeal skeleton of the first-stage maggot in the Masicera- 

 tidcB or leaf-ovipositing forms, in which his structure has reached 

 the extreme of reduction and consolidation. This argues for a 

 high degree of specialization here, of longer standing than that of 

 the leaf-larviposition forms. The conclusion is borne out by 

 the elongate intestiniform uterus, microscopic size of the egg, 

 and the remarkably divergent host relations whereby it becomes 

 necessary fully to develop the maggot within the chorion without 

 allowing it to escape therefrom until it shall have arrived in the 

 alimentary canal of the host, notwithstanding that it may remain 

 for a considerable time deposited and unswallowed. Such pro- 

 visions mark an extreme specialization of very long standing. 

 How these microscopic eggs could have originally arisen from a 



