LETTER XXXIV. 
EXTERNAL ANATOMY OF INSECTS. 
THE HEAD, AND ITS PARTS. 
BEFORE I confine my observations to the head of in- 
sects, which I propose to consider separately in the pre- 
sent letter, I must premise a few words upon their body 
in general, or rather its crust, or external integument. 
In this we may notice its substance, general form, sculp- 
ture, pubescence, and composition. 
i. I have already noticed the substance of this integu- 
ment in the preparatory states of insects*; I shall not, 
therefore, here repeat what I then said, but restrict my- 
self chiefly to the consideration of it as it is found in their 
last state, in which it is usually firmer than in their pre- 
vious stages of existence. In this respect, however, it 
varies much in the different Orders, and even in the dif- 
ferent genera of the same Order. In some Coleopterous 
insects, for instance, it is very hard, and difficult to per- 
forate ; while in others it is soft, flexible, and a pin easily 
passes through it®. And in general, from a substance 
* See above, p. 110, 243—. 
> Many species of Hister, Curculio L., Doryphora are extremely 
hard; while Cantharis, Meloe, and Telephorus, are very soft. 
