2S COMPARATIVE ANATOMY BKFORK CUVIER 



through all Bichat's work ; it receives classical expression in 

 his Rcchcrc/tcs Physiologiques snr la \'ic ct In Mori (iSoo). 

 The plant and the animal stand for two different modes 

 of living. The plant lives within itself, and has with 

 the external world only relations of nutrition ; the animal 

 adds to this organic life a life of active relation with 

 surrounding things (3rd ed., 1.^05, p. 2). "One might 

 almost say that the plant is the framework, the foundation, 

 of the animal, and that to form the animal it sufficed to cover 

 this foundation with a system of organs fitted to establish 

 relations with the world outside. It follows that the functions 

 of the animal form two quite distinct classes. One class 

 consists in a continual succession of assimilation and excre- 

 tion ; through these functions the animal incessantly trans- 

 forms into its own substance the molecules of surround- 

 ing bodies, later to reject these molecules when they have 

 become heterogeneous to it. Through this first class of 

 functions the animal exists only within itself; through the 

 other class it exists outside ; it is an inhabitant of the world, 

 and not, like the plant, of the place which saw its birth. The 

 animal feels and perceives its surroundings, reflects its 

 sensations, moves of its own will under their influence, and, as 

 a rule, can communicate by its voice its desires and its fears, 

 its pleasures or its pains. I call organic life the sum of the 

 functions of the former class, for all organised creatures, 

 plants or animals, possess them to a more or less marked 

 degree, and organised structure is the sole condition necessary 

 to their exercise. The combined functions of the second 

 class form the ' animal ' life, so named because it is the 

 exclusive attribute of the animal kingdom " (pp. 2-3). 



In both lives there is a double movement, in the animal 



life from the periphery to the centre and from the centre to 



the periphery, in the organic life also from the exterior to the 



interior and back again, but here a movement of composition 



and decomposition. As the brain mediates between sensation 



ami motion, so the vascular system is the go-between of 



the organs of assimilation and the organs of dissimilation. 



The most essential structural difference between the 



ins of animal life and the organs of organic life is, in 



man and the higher animals at least, the symmetry of 



