198 THE NATURE AND ORIGIN OF LIFE 



dition, but rather in conditions such that the being continues 

 to live. This singularly limits future possibilities. In fact, 

 observation proves that the possible variations in a living 

 being cannot go beyond certain bounds under pain of death. 

 A young fox will become an adult fox and certainly not a 

 herring or a horse. But this has nothing surprising in 

 connexion with what we already know. A fox that con- 

 tinues to live can do nothing but " fox " and, while foxing, 

 it builds up a fox by functional assimilation. 



In other words, the conservation of life or renewal of 

 the interior medium can be carried on only by the play of 

 the animal's pre-existing organs, by the functioning of the 

 tools which constitute its body. These tools, while func- 

 tioning, develop themselves by functional assimilation. 

 Under certain circumstances, one of them may develop 

 itself more than another, which introduces into the economy 

 of the individual quantitative variations. But even such 

 quantitative variations are limited by the general co-ordi- 

 nation ; the hypertrophy of one organ and the atrophy of 

 another cannot pass certain limits without involving the 

 animal's death. 



This is why we have the right to say that the heredity 

 of the egg determines in a certain measure the future of the 

 being which comes from it. We cannot foresee if the being 

 will live or die ; but we can assert that, if it lives, its varia- 

 tions will be comprised within certain limits. In particular, 

 we can assert that the being will belong by its morphologi- 

 cal characters to the species which furnished the egg from 

 which it issues. 



In proportion as the being grows old, at least in species 

 with a persistent skeleton like the human species, the varia- 

 tions allowed to it become more and more restricted. The 

 skeleton which fixes all the parts of the body makes of it 



