44 DEFINITION OF THE TERM INSECT. 



skeleton of the animals just named; and that even in those 

 in which the body appears to have no such segments, as 

 in many of the Mites (Acarus L.), they are to be found in 

 the limbs. This last circumstance, to have externally 

 jointed legs, is the peculiar and most general distinction by 

 which the Insecta of Linne, including the Crustacea, may 

 always be known from the other invertebrate animals a . 



If we proceed further to examine the substance of this 

 crust or covering, though varying in hardness, we shall 

 find it in most cases, if we exclude from our considera- 

 tion the shells of the Mollusca, &c, better calculated to 

 resist pressure than that of the majority of animals that 

 have no spine. In all the invertebrate tribes, indeed, the 

 muscles, there being no internal skeleton, are attached 

 to this skin or its processes, which of course is firmer 

 than the internal substance; but in insects it is very often 

 rigid and horny, and partially difficult to perforate, sel- 

 dom exhibiting that softness and flexibility which is found 

 in the cuticle of birds and most quadrupeds. From this 

 conformation it has been sometimes said, that insects 

 carry their bones on the outside of their body, or have 

 an external skeleton. This idea, though not correct in 

 all respects, is strictly so in this — that it affords a general 

 point of support to the muscles, and the whole structure 

 is erected upon it, or rather I should say within it. The 

 difference here between Insects and the Vertebrata seems 

 very wide; but some of the latter make an approach to- 

 wards it. I allude to the Chelonian Reptiles ( Testudo L.), 



a The Annelida have, however, sometimes jointed organs, which 

 facilitate their progressive motion whether vermicular or undulatory ; 

 but they cannot be deemed legs, since they neither support the body 

 nor enable it to walk, &e. Latreille Anim. invertebr. Artie. 126. Ann. 

 du Mus. 1821. 



