HEREDITY 197 



Selection is an adaptation most pronounced, and 

 heredity is the continuity of the same adaptation : 

 so that the great problem of evolution is reduced to 

 two terms, adaptation and medium, which is the 

 parallelism through which it happens that all 

 organised beings are the reflex, the echo of natural 

 mechanics. Without light, sight would not exist, 

 as without sound there is no hearing. The 

 bronchial tubes, divided and subdivided in order 

 that the blood and air may effect the necessary 

 contact, obey the same principles by which the 

 roots of trees cross large tracts of land in order to 

 reach water. 



So long as the cosmic medium, upon which the 

 world in which we live depends, undergoes no 

 change, as little subject to change will be the 

 organisation of the bodies that depend upon it, for 

 they are its natural and direct consequence. 



Animals on reproduction repeat the same form 

 and structure, in the first place because the same 

 conditions persist in the medium ; because the 

 parallelism is the same, the rhythm continues, 

 and they continue as the faithful reproduction of 

 universal mechanics. Medium and organisation 

 are two terms that are reinforced by a parallelism 

 of millions of ages, whose energy obeys the prin- 

 ciple of continuity and rhythm of force. 



Silk, which constitutes a most important industry, 



