82 PHILOSOPHY OF ZOOLOGY. 



horses ; in the form of powder, from the skins of parrots ; 

 and entire like a sheath, from serpents and the caterpillars 

 of insects. 



The cuticle exhibits very remarkable differences in re- 

 gard to consistence. In those animals which live on the 

 land, it is more rigid in its texture, and scaly and dry on 

 its surface, than in those which reside in the water. In 

 aquatic animals, it is in general smooth, often pliable ; and, 

 in many cases, its texture is so soft and delicate, that it ap- 

 pears like mucus. It assumes, likewise, other appearances, 

 such as scales, nails, shells and plates, which deserve the 

 attentive consideration of the naturalist, as furnishing him 

 with important characters for the arrangement of animals. 



2. Mucous web. This has been named in honour of the 

 discoverer rete Malpighii : and likewise corpus mucosum 9 

 or rete tnucosum. It occurs immediately underneath the 

 cuticle, from which, in general, it may be easily disjoined ; 

 but it is often so closely attached to the true skin below, as 

 not to be separated even by maceration in water. 



It presents more obvious appearances of organization 

 than the cuticle, and consists of soft vascular tissue. It 

 varies in thickness in different species, and even in diffe- 

 rent parts of the same individual. It is regenerated more 

 slowly than the cuticle, at least its colour, after an injury, 

 is more pale, inclining to white. In the parts of those ani- 

 mals which have been reproduced after amputation, as the 

 head and horns of snails, the new portions seldom present 

 the same intensity of colour as the old ones. Its chemical 

 constitution is unknown. It is more or less coloured, accord- 

 ing to the species or variety ; and, indeed, is that portion 

 of the skin in which the colour resides. In man, the other 

 layers of the integuments are transparent or colourless ; 

 while this layer is white in the European, black in the 

 Ethiopian, and copper-coloured in the American. 



