INSECTA. 239 



otherwise inevitable processes by which dead animal matter reverts 

 to its primitive elements. Insignificant indeed do these larvae seem 

 to be in the scale of nature, yet Linnaeus* used no exaggeration 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 organising 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 require the sus- 

 pension of all the ordinary actions of life. The larval skin is 

 thrust off by the new integument of the new organs, and is con- 

 verted into an opaque brown case : the inclosed insect shrinks partly 

 by the loss of exhaled fluids, partly by the condensation of its former 

 soft tissues into the new and firm substances constituting the legs 

 and wings. A large and distinct head is now developed, with eyes, 

 antennae, and instrumenta cibaria ; all which processes are carried 

 on in the quiescent concealment of the opaque and dark exuvium, 

 like the analogous processes in the egg of the Orthopterous, and 

 within the womb of the pupiparous, insect. The active carnivorous 

 vermilarve returns, in fact, a second time to the state of an ovum, 

 when it becomes the coarctate pupe ; and the perfect insect, splitting 

 its cerement, issues forth as by a second birth. 



The larvae of the gnats (Culex) and crane-flies {Tipidce) have a 

 distinct corneous head with jaws : the former have a plumose anal 

 coronet, by which they sustain themselves at the surface of the 

 water : the orifices of the tracheae are placed in the middle of this 

 coronet. A pair of tracheal tubes extend through the long, slen- 

 der, and extensile anal canal of the aquatic grub of the Musca 

 (Bristalis) tenax. By this mechanism, which is analogous to the 

 tube of the diving bell, the rat-tailed larva can derive its requisite 

 supply of air from the surface while groping for food in the mud at 

 the bottom of the pool. 



The economy of the Hymenoptera and the various circumstances 

 attending the development of their apodal larvas form the subjects of 

 a long chapter in the History of Insects. 



I must be governed in the unavoidably brief selection from this 

 rich storehouse of intereresting facts by the specimens which Hunter 

 has left for our instruction. Here (exhibiting the preparation No. 

 3104.) we have a portion of the nest of a social hymenopterous 



* Systema Naturae, Musca carnaria. 



