162 FROM LAMARCK TO ST. HILAIRE. 



ployment of an organ becoming constant under the 

 influence of certain habits, gradually impoverishes 

 the organ and ends by causing it to disappear en- 

 tirely." In the Discours preliminaire, he outlines 

 his work as divided into three parts. The first is 

 to treat of the subject in general, of methods of re- 

 search, of artificial distinctions raised by man in 

 classification, of the real meaning of the term ' spe- 

 cies,' of the proofs of the 'degradation' 1 (Evolution) 

 of organization from one end to the other of the 

 animal scale, of the influences of environment and 

 habit as causes favouring or arresting the develop- 

 ment of animals, of the natural order and classifica- 

 tion of animals. In this first section his whole 

 theory of Evolution is to be expanded, which we 

 will examine later. In the second part, he considers 

 the essential phenomena and physiological condi- 

 tions of life or ' orgasme ' and irritability, of the 

 peculiarities of cellular tissue, of the conditions 

 of spontaneous generation. This section covers 

 what we would now term the general principles of 

 Biology. The third part is devoted to the develop- 

 ment of the nervous system, sensation, action, and 

 intelligence, including a theory of the origin and 

 formation of the nerves, and of the development of 

 mental faculties and ideas, lower and higher. Here 

 he treats of the relation of the mind of man to that 

 of the lower animals. 



Lamarck's general philosophy of Nature comes 

 forth here. He is, first of all, an advocate of the 



