AQ 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 Orthoptera, Hemiptera, Neuroptera, and 
especially Lepidoptera, a large proportion would be found 
to exceed three lines in length. Neither can it be af- 
firmed of extra-EKuropean 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 of vertebrate animals, it affords 
less assistance in separating them from the znvertebrate 
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: 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, J 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, 
