24 THE DOCTRINE OF DESCENT. 



II. 



The Animal World in its Present State. 



In order to approach the doctrine of Descent, and to 

 prepare for its necessity, we purpose next to pass in 

 review a main part of its object, — the present condition 

 of the animal world in its general outlines. Organisms, 

 as every one may see, are distinguished from ^nimate 

 bodies by a certain mutability of existence ; a sequence 

 and alternation of phenomena, combined with constant 

 absorption and expulsion of matter. These changes, 

 which are ultimately molecular motions, and are there- 

 fore calculable, definable, and susceptible of investiga- 

 tion, take place in particles in a state of saturation — that 

 is to say, soaked in water and aqueous fluids ; and this 

 peculiar, yet purely mechanical condition, suffices for the 

 explanation and comprehension of many of the neces- 

 sary phenomena of life. Experience shows that this 

 capacity for saturation, and this mobility, essentially 

 characterize the combinations of carbon ; and the sum 

 of these motions and displacements, of which a great 

 part has already been susceptible of mathematically cer- 

 tain investigation, is termed Life. 



Now it is impossible to resist the impression that 

 there are simple and composite, lower and higher, living 

 beings ; and we likewise feel, more strongly than words 

 will express, a certain antithesis between the plant and 



