228 



ANATOMY. 



it is brown or black, as also in all black insects. The variegated 

 colours of these do not therefore proceed from the rete mucosum, but 

 from the hairs clothing the surface. In spirits of wine it readily 

 dissolves, and thereby distinguishes itself from the second layer, which 

 is not affected by this fluid, and is uniformly black or brown *. This 

 second layer is always covered by the first, and participates no 

 otherwise in the colouring than by its darkness or depth adding to 

 the intensity of the colour above it. In bright yellow, red, or white- 

 coloured spots, it passes over naturally into this lighter colour. 



The third and thickest layer of the general integument, the true 

 leathery tunic (corium), betrays itself by its want of colour and 

 peculiar structure. It consists, namely, of several layers of crossing 

 fibres, which form a light web, which, upon a careful investigation, 

 again admit of separating into several stratifications. Straus some- 

 times distinguished three, at others five, such strata. In the elytra of 

 beetles (for example, Dyticus, Hydrophilus), there are delicate canals 

 between these layers, in which the formative juice seems to flow, 

 when the still small and short elytra of a just-developed beetle 

 distend themselves ; it is also in this leathery skin that the bulbs lie 

 which surround the roots of the hair. It is from this skin that the 

 roots of the hair derive their nutriment. A perforated point, many of 

 which are displayed upon the surface of a multitude of insects, is a 

 partial deficiency of this leathery skin. The epidermis and mucous 

 rete consequently sink down, and thus a hollow is formed upon the 

 surface. At the same time, the sinking of the harder epidermis forms 

 a point to which the layers of the corium are attached ; thence is it 

 that the points stand generally in rows between two fibres of the 

 corium, for example, the three rows of punctures in the large water 

 beetles. (Dyticus marginalis, &c.) 



161. 



We must consider the spines, hairs, and scales which cover the 

 surface of many insects, as portions of the integument, and, as it were, 

 partially separated parts. All three are like the horny substances of 

 the higher animals, for example, the claws and nails, not processes of 



* According to Straus, p. 16. But if the brightly-coloured layer dissolves in spirits of 

 wine, Low is it ,that so many insects, namely, the blue metallic or aeneous ones, retain 

 Lir colour in this fluid, and onlv some red or yellow ones lose it? 



