42 DEFINITION OF THE TERM INSECT. 



human race, since they keep within due bounds the va- 

 rious destroyers of our produce. 



The number of minute species of insects seems greatly 

 to exceed that.of large ones, at least in Europe, of which 

 it may be asserted probably with truth, that two-thirds 

 are under a quarter of an inch in length, and one-third 

 not exceeding much a duodecimal of it. It might hold 

 good perhaps in Coleoptera, Hymenoptera, Diptera, and 

 Aptera : but in Qrthoptera, Hemiptera, Neuroptera, and 

 especially Lepidoptcra, a large proportion would be found 

 to exceed three lines in length. Neither can it be af- 

 firmed of extra-European species, of those at least pre- 

 served in cabinets, amongst which it is rare to find an 

 insect less than the fourth of an inch long. This, how- 

 ever, must probably be attributed to the inattention of 

 collectors, who neglect the more minute species. 



Though size forms a pretty accurate distinction between 

 insects and the great bulk ofcvertebrate animals, it affords 

 less assistance in separating them from the invertebrate 

 classes, which are of every size, from the monstrous bulk 

 of some Cephalopoda (cuttle-fish) and Mollusca (shell- 

 fish, &c.) to the invisible infusory animalcule i but ex- 

 ternal characters, abundantly sufficient for this purpose, 

 may be drawn from the general covering, substance, form, 

 parts, and organs of the body. As I shall enter into pretty 

 full details upon this subject when I come to treat of the 

 external anatomy of insects, I shall here, therefore, only 

 give such a slight and general sketch of the distinctions 

 just mentioned, as will answer the end I have in view. I 

 must here repeat what I have before observed, and what it 

 is necessary that you should always bear in mind, namely, 



