106 PHILOSOPHY OF ZOOLOGY 
place in the state of health, are questions to which no satis- 
factory answer has been given. 
In the view which has been taken of the skin, its lay- 
ers, appendices and functions, no characters have presented 
themselves of any great value in the construction of primary 
divisions in the classification of animals. The cuticle and 
the corium, perhaps, exist in all animals. In some, the 
mucous web is the seat of colour; but when this layer can 
no longer be detected, we still find the remaining layers of 
the skin, and their appendices, presenting even a bnilhant 
display of colours, intimating, that its absence has been 
So 
supplied, by the action of some of the other layers. ‘The 
muscular web is present in some, and almost absent in other 
animals, even of the same class; and the same observation 
holds true with respect to the cellular web. 
Hair is not peculiar to the mammalia. It is found on 
birds and even worms. Feathers, however, are peculiar to 
birds, as nothing analogous has been observed on the bodies 
of other animals. Horns, scales, shells, and crusts, are 
found on animals so widely different in form, structure and 
habits, as to forbid the employment of the characters which 
they furnish, in the construction of divisions of a high or- 
der. Lately, however, Cuvier has distributed animals into 
four divisions ; Vertebral, Molluscous, Articulated and Ra- 
diated. The cxternal character of the Articulated division, 
in which insects, lobsters and worms are included, 1s found- 
ed on the appearances presented by the skins of the ani- 
mals which it includes. In these, the body is either in 
whole or m part formed into rings, by means of transverse 
plates of the skin, or the skin contains scales or crusts, placed 
like rmgs on the body, or some of its parts. 
If the arrangement of the skin and its appendices, in 
whole or in part, ito rings, was exclusively confined to 
those animals which are regarded as belonging to the annu- 
