GENERATION OF INSECTS. 425 



iqDon wliich there is not the least indication of the parts of the per- 

 fect 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, coalescence, arrangement, and trans- 

 formation of the hyaline nucleus and germ-cells is vermiform. In all 

 insects the embryo first manifests itself as an apodal smooth Ento- 

 zoon ; next as an Annellide of thirteen rings : in all insects the first 

 segment is quickly modified, and the mouth established ; and in this 

 state the larva is excluded in some insects, as the bee and fly, without 

 any appendages being developed ; and in the bee before the com- 

 pletion of the intestinal canal. 



The maggots of the order Dlptera and Hymejioptera typify the 

 Entozoa ; they have no distinct scaly head, and no thoracic legs ; 

 lience they have been termed " vermilarves." Those of the Diptera 

 and of the Ichnemnonidce represent the parasitic worms, not only in 

 structure, but in habits ; the larvaa of the Gastorophili called " bots," 

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

 animals. The larvas of the Anthorugia canicularis may be, in like 

 manner, considered as entozoa of the human subject. There is a 

 breeze-fly ( CEstrus honmiis), which deposits its egg beneath the inte- 

 gument 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 vermilarves, as those of (Estrus Bovis and (Est. Tarandi, are 

 developed beneath the integument or in the nasal sinuses of the Ru- 

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

 modes of animal life than that of the parasitic Entozoa we can com- 

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

 condition of whose existence is the putrid fiesh of higher organised 

 beings. Here, however, the development of helminthoid larva has 

 been beneficially ordained in order to neutralise the noxious efifects of 

 the otherwise inevitable processes by which dead animal matter 

 reverts to its primitive elements. Insignificant, indeed, do these 

 larvie seem to be in the scale of nature, yet Linnaeus used no' exag- 

 geration when he averred that three flesh-flies would devour the 

 carcase of a horse as quickly as would a lion. The assimilative 

 power is so great in the meat-maggot, that it will increase its own 

 weight two hundred times in twenty-four hours. 



But the developmental energies are not exhausted by the rapid 

 growth of the larva ; some remain to be exercised in the formation 

 of the new and peculiar organs which entirely change the form and 

 properties of the creature. For this exercise they usually require 



