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/cm, sculp- 

 ture, "pubescence, and composition. 



i. I have already noticed the substance of this integu- 

 ment in the preparatory states of insects a ; 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 5 . And in general, from a substance 



a See above, p. 86, 110,243—. 



b Many species of Hister, Curculio L ., Doryphora Illig. are ex- 



