DIPTERA : TRANSFORMATIONS. 



417 



dergo in their passage to the perfect state, there is less diver- 

 sity than in the organization of the perfect insect. Insects 

 in general are oviparous, but there are of course exceptions 

 to this rule, and two of the most remarkable are to be found 

 in this order. The blowfly forms one of these exceptions 

 in which the eggs are hatched in the body of the parent, and 

 produced in a Hving state. The other occm's in the forest- 

 flies {HippoboscidcB), in which group not only are the eggs 

 hatched within the body of the female, but the larva there 

 acquires its full growth, and assumes the pupa state, being 

 ejected from it in the shape of an egg as large as the abdomen 

 of the parents, and from which the perfect insect, instead of 

 the larva, makes its escape. 



The larvae of the Diptera in general off'er so great a sim- 

 plicity of structm'e, as to cause an uniformity of appearance ; 

 nevertheless, those which reside in the water are more diver- 

 sified in their characters, being furnished with organs of 

 nutrition and respiration very unlike those of the terrestrial 

 larvae : this is especially the case in the common gnats (fam. 

 CuUcidcB), and the cuUciform Tipulidte, {Chironomus, &c.) 



In passing to the 

 pupa state, these 

 larvae adopt two 

 principal modes. In 

 the greater number 

 there is no shedding 

 of the skin ; the skin 

 of the larva hardens, 

 contracts, and be- 

 comes an oval co- 

 Larva, Pupa, and perfect Chironomus, magnified. ': COOU within which 



the pupa is disengaged, appearing at first merely as a gelat- 

 inous mass, but afterwards exhibiting in some degree the 

 diff^erent parts of the perfect insect, the eyes and wings being 



