ENTOMOLOGY. 87 



a glutinous secretion without the assistance of threads. 

 Saw-flies, and some other Hymenopterous tribes, 

 construct a double cocoon, the outer one not united 

 to the interior, but inclosing it as the shell of a nut 

 does its kernel. Many larvae dwell in habitations 

 which they form with much skill and labour, to de- 

 fend their tender bodies, and these likewise serve as 

 a ready and efficient protection for the pupa. Such 

 are the cases of the May-flies (JPhryganece) which 

 are common in slow flowing streams, and curious on 

 account of the materials with which they are covered ; 

 the mantles of many leaf-rolling caterpillars, and the 

 portable tents constructed by others. Dipterous 

 larvae are frequently converted into pupae within their 

 own skin, which changes its form and becomes of a 

 more rigid texture for the purpose of affording it 

 more effectual protection. The change to a pupa 

 does not always take place immediately after the 

 preliminary arrangements are completed, although 

 the contrary is the general rule ; a period of inactivity 

 often ensues ; and some caterpillars remain unaltered 

 within their cocoons for months together. 



Pupa. This is the most general term applied to 

 insects in the third stage of their existence, that, 

 namely, which intervenes between the larva and 

 imago. It was suggested by their appearance, which 

 resembles that of a child wrapped up in swaddling 

 clothes, all the parts being closely folded down, and 

 enclosed in a general envelope. It is, therefore, very 

 applicable to the majority of them, as they are com- 

 pletely dormant and inert, incapable either of moving 



