238 LECTURE XVIII. 



of sense or locomotion in the perfect insect, and which organs are 

 therefore comparatively free, although the pupa be quiescent. La- 

 raark called such pupae " Mumiae." 



In the obtected Lepidoptera the growing wings, antlia, antennee, 

 and thoracic legs are only partially covered by the pupal integument, 

 being lodged in recesses on its inner surface, which make correspond- 

 ing projections on its exterior, where their form and position may 

 thus be recognised. 



In the coarctate metamorphosis of the Diptera, the larva sheds its 

 last skin before the growing legs and wings have impressed their 

 forms upon it, and the exuvium constitutes an egg-shaped horny case, 

 upon which there is not the least indication of the parts of the perfect 

 insect. 



Under whatever form the insect be excluded from the egg^ if we 

 trace its development further back, we shall find that the tendency of 

 the mysterious multiplication, arrangement, and transformation of the 

 hyaline and vitelline particles is vermiform. In all insects the em- 

 bryo first manifests itself as an apodal smooth Entozoon ; next as an 

 anellide of thirteen rings : in all insects the first segment is quickly 

 modified and the mouth established ; and in this state the larva is ex- 

 cluded in some insects, as the bee and fly, without any appendages 

 being developed. 



The maggots of the order Diptera typify the Entozoa ; they have 

 no distinct scaly head, and no thoracic legs ; hence they have been 

 termed " vermilarves." They represent the parasitic worms not only 

 in structure but in habits ; the larvae of the Gasterophili called "bots," 

 pass that stage of their existence in the alimentary canal of higher 

 animals. The larva of the Anthorugia canimilaris may be in like man- 

 ner considered as entozoa of the human subject. There is a breeze- 

 fly (CEstrus homi?iis)* which deposits its egg beneath the integu- 

 ment of the living body, and its larva there grows and flourishes like 

 the Filaria in the cellular tissue. The larva of a species of Cuterebra 

 occasionally finds its way into the human frontal sinus. Other vermi- 

 larves, as those of the CEstri Bovis and Tarandi^ are developed be- 

 neath the integument or in the nasal sinuses of the Ruminants 

 indicated by their specific names. I know not to what other modes 

 of animal life than that of the parasitic Entozoa we can compare the 

 habits of the voracious maggots of the flesh-fly, the essential condi- 

 tion of whose existence is the putrid flesh of higher organised beings. 

 Here, however, the development of helminthoid larva has been bene- 

 ficently ordained in order to neutralise the noxious effects of the 



* Howship, Proceedings of the Royal Society, March 21, 1833. 



