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 isin 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, 
or rete mucosum. It oceurs immediately underneath the 
cuticle, from which, in general, it may be easily disjomed ; 
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 mjury, 
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 m which the colour resides. In man, the other 
layers of the integuments are transparent or colourless ; 
while this layer is white im the European, black in the 
Ethiopian, and copper-coloured in the American. 
