i66 



THE MECHANISM OF LIFE 



ment of more complicated forms as the conditions changed on 

 the surface of the globe. Darwin shows how heredity and 

 natural selection tend to accentuate the variations which are 

 favourable to existence. Haeckel demonstrates the parallelism 

 between ontogenesis and philogenesis — between the successive 

 forms in the evolution of the embryo and the successive forms 

 of the individual in the evolution of a race. These are great 

 and admirable conquests of the human intelligence, they have 



FlG. 63. — Marine forms of osmotic growth. 



demonstrated the first appearance and the progressive evolution 

 of living beings; it now only remains for us to explain them. 



The doctrine of evolution, while enforcing the fact of 

 spontaneous generation and progressive evolution, gives us no 

 hint as to the physical mechanism of such generation. It does 

 not tell us by what forces, or according to what laws, the simpler 

 forms of life have been produced, or in what manner differences 

 of environment have acted in order to modify them. The 

 doctrine asserts the simultaneous variations in organic forms 

 and in the physical influences which produce them, but says 



