400 EXTERNAL ANATOMY OF INSECIYS. 
tegument; under which term I would include the diffe- 
rent layers of which it consists, and its articulation. 
1. With respect to the first of these circumstances, 
the Jayers of which the integument consists, it seems to 
exhibit some, although not an exact, analogy with the 
skin, rather than the skeleton, of the vertebrate animals?. 
In these last, the skin is stated to consist of four layers. 
Of these the exterior one is the epidermis, or scarf-skin: 
under this is the rete mucosum, or mucous tissue, which 
gives its colour to the skin; next follows the papillary 
tissue formed by the extremities of the nerves, and in 
which the sense of touch principally resides; the Jast and 
innermost layer is the skin proper, or leather, called Der- 
mis, Derma, or Corium>. Two of these layers M. Cu- 
vier assigns to insects. They have, he observes, in every 
state, a true epidermis*; and in their state of larva he 
finds that the infinite variety of colours that so adorn 
many of them is produced by a mucous substance ob- 
servable between the epidermis and the muscles‘: this 
seems analogous to the rete mucosum. ‘To this, dried 
and mixed with their horny substance, he attributes also 
the colours of the perfect insect: “for,” says he, ‘when 
the Lepidoptera are in the chrysalis, the little coloured 
scales which are to ornament their wings, are then in a 
state of mucosity similar to that which is found under the 
skin of the caterpillar. The colours of the Arachnida,” 
he goes on, “are also due to this mucosity: it is disco- 
verable under the skin, and has the appearance of mi- 
nute glandular points of which the shades vary consider- 
® Anat. Compar.i. 119. > Toid. ii. 540. 
§ Ibid. 547. 4 Tbid. 553. 
