ENTOMOLOGY. 
97 
understood in what its peculiar characters and attri- 
butes consist 
The external integument,, or crust of insects, oc- 
cupies the place of the skin in higher animals, as it 
forms a general envelope for all the parts ; but, unlike 
the skin, it is of a rigid and horny consistency. In the 
latter particular it is liable to a good deal of varia- 
tion, being sometimes homy and inflexible, (as in 
beetles,) at other times comparatively soft, and yield- 
ing to the slightest pressure. In all cases, however, 
it has sufficient strength to give effectual support to 
the muscles, which are attached to its interior surface, 
thus serving the same purpose as the bones of the 
vertebrata ; on this account, insects have been some- 
times described as bearing their skeleton externally. 
Besides resembling the true skin in its situation, it 
is found to display further conformity to it, in con- 
sisting of three principal layers, viz. the epidermis or 
exterior layer, the rete mucosum, arid lastly, the 
leathery tunic, sometimes called the dermis or corium. 
The first of these is smooth, shining, and generally 
uncoloured, for the most part thickly perforated with 
small holes, through which the hairs rise to the sur- 
face. The mucous tissue ( rete mucosum ) consists, 
according to Strauss, of two layers, the upper of which 
is closely attached to the epidermis, and in this reside 
the brilliant colours with which so many insects are 
adorned.* The third layer is without colour, and 
* Except, of course, the Lepidoptera, in which the colours, 
D« is well known, are produced by a superficial covering 
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