80 PHILOSOPHY OF ZOOLOGY. 



The proportion between the solids and fluids, is not only 

 remarkably different in different species, but in the same 

 species in the various stages of growth. 



Having now taken a general view of the substances which 

 enter into the composition of animal bodies, and the various 

 textures or tissues which these form, it is our intention to 

 proceed to consider the frame itself, and to examine the 

 various organs, or system of organs, of which it consists, 

 and the uses to which these are subservient in the animal 

 economy. The order in which we proceed, may appear 

 to be deficient in logical precision ; but it is impossible 

 to investigate the organs, in connection with their functions, 

 without adopting a method in some degree arbitrary. The 

 skin, however, obviously demands our first attention. 



CHAP. VI. 



OX TIIK CUTANEOUS SYSTEM, ITS STRUCTURE, APPENDICES, 

 AND SECRETIONS. 



W HEN treating of the characters by which organized bo- 

 dies might be distinguished from inorganic matter, it was 

 stated, that the former always possess a skin or common 

 integument. This organ, as it exists in animals, is now to 

 be the subject of our consideration. 



1. STRUCTURE OF THE SKIN. 



Animals present remarkable differences with regard to 

 the size, the shape, and the number of their parts ; but 

 they all agree in possessing an exterior covering, or skin, to 

 modify their surface, regulate their form, and protect them 

 from the action of the surrounding elements. In the more 

 perfect animals, this organ consists of the following parts : 



