106 PHILOSOPHY OF ZOOLOGY. 



place in the state of health, arc 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 brilliant 

 display of colours, intimating, that its absence has been 

 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, arc 

 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, CUVIEU has distributed animals into 

 four divisions ; Vertebral, Molluscous, Articulated and Ra- 

 diated. The external character of the Articulated division, 

 in which insects, lobsters and worms are included, is 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 in part formed into rings, by means of transverse 

 plates of the skin, or the skin contains scales or crusts, placed 

 like rings on the body, or some of its parts. 



If the arrangement of the skin and its appendices, in 

 whole or in part, into rings., was exclusively confined to 

 those animals which are regarded as belonging to the annu- 



