200 PTILOTA. 



The existence and the number of legs of the larva, the 

 permanent or variable form of the head, the comparative 

 structure of the organs of the mouth with those of the 

 imago, the number of the spiracles aud disposition of the 

 tracheae, the moultings of the skiu, and the quiescent or 

 active state of the pupa, are all important considerations, 

 upon which the distribution of insects from the characters of 

 their metamorphosis may be effected. 



Hence the Lepidoptera (figs. 35, 36, and 37), are dis- 

 tinguished by the number of legs, scaly head, &c. of the 



Fig.. 38. 



caterpillar (Eruca Latreille), and the obtected, or, a* 

 I^atreille prefers calling it, the mummy-formed pupa (Chry- 



Urv ; 42, Pap. IncompleU ; 43, I m. t o of < hn-.omclm popali. 



salts Latreille). The Diptera (figs. 38,39, and 40) are dis- 

 tinguished by their worm-like larva; (Vermilarva Latreille), 



