STATES OF INSECTS. (Larva.) 155 
thread that forms the cocoon inclosing the pupa*. Pro- 
vidence has many different ways of performing the same 
operation. From the structure of the oral organs of 
these animals, the silk could not conveniently be fur- 
nished by the mouth; the Allwise Creator has therefore 
instructed and fitted them to render it by a spinneret at 
the other extremity of the body. 
The respiratory anal appendages of many Dipterous 
larvee will be fully described in a subsequent Letter: I 
shall therefore now only further observe upon this subject, 
that although there is seldom any alteration in the form of 
these appendages, &c. in the same species, the caterpil- 
lars of two moths (Cerura Vinula and Aglia Tau), how- 
ever, are exceptions. The former, when young, has two 
hairy projecting ear-like protuberances, which it entirely 
loses, as I have myself observed, before it assumes the 
pupa; and the latter, in like manner, after its third 
change of skin, is deprived of its bent thorn-like points 
which attend it when young’. It is remarkable that 
these last larvae, when just excluded from the egg, are 
also entirely destitute of these appendages; they soon, 
however, appear, from slight elevations which mark their 
situation, and rapidly acquire their usual form *. Changes 
of a similar kind, hitherto unobserved, may probably 
take place in other species. 
ii. Figure. I am next to consider the general figure 
or shape of larvae. All of them, with but few exceptions 4, 
agree in having a body more or less constricted at inter- 
* Reaum. ili. 384, vi. 366. ¢. xxxii. f. 7, 8. 
> Ros. iii. é. Ixviii. f. 1. Meinecken Naturf. vi. 120. 
© Thid. xiii. 175. 
¢ In the larva of Dolerus ? Cerasi, and some ethers, no traces of 
