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 ( Phryganece) 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 
