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 vestigate 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. 
ON THE CUTANEOUS SYSTEM, ITS STRUCTURE, APPENDICES, 
AND SECRETIONS. 
Wien 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 ergan, as it exists in animals, is now to 
be the subject of our consideration, 
1. SrructTurReE 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 : 
