94 PRIMITIVE FORMS OF LIFE 



stored-up hereditary characters which they received from the 

 ovum. 



Armogenesis has consequently only a secondary importance 

 in the evolution of organisms. Not so, however, tachygenesis. 

 We have demonstrated elsewhere that it furnishes us with an 

 explanation of the resemblance of the evolutionary develop- 

 ment in the female and the male cells. 1 Its influence on 

 the morphology of living beings is just as great. By virtue 

 of the independence of the structural cells giving rise to the 

 tissues, the organs, and even the areas of the body, this 

 influence affects the different parts in various ways, modifies 

 their relationships and their proportions, and induces trans- 

 positions and fusions, to which Etienne Geoffrey Saint-Hilaire 

 had already appealed when he tried to explain how unity in 

 the plan of composition did not necessarily exclude variety 

 in the details of organization. It thus becomes an instrument 

 of modification, all the more powerful since in the course of 

 embryonic development a veritable struggle for existence 

 takes place, in a narrow field of battle, so to speak, between all 

 the structural cells and all the tissues and organs which they 

 constitute as well as between the various body areas themselves. 



If armogenesis tends to bring embryos into intimate relation 

 with the environment in which they develop, tachygenesis, 

 on the contrary, tends to alter these relations more and more, 

 and to accentuate the dissociation between causes and effects 

 which heredity in its purely conservative aspect had already 

 begun to accomplish. Fortunately, this dissociation is generally 

 gradual. In each series the lower forms most frequently present 

 a patrogonic form of development, in which essential characters 

 are conserved in the tachygenetic forms. This permits us, on 

 the one hand, to distinguish the links which connect characters 

 and the causes capable of producing them, and, on the other 

 hand, to eliminate, by explaining the facts upon which they 

 might be based, any possible objections to the inferences 

 suggested by the analysis of the modes of development most 

 closely akin to patrogony. This work of weeding out and 

 classifying embryogenetic phenomena had never been done 

 in a methodical manner until I attempted it in the embryo- 

 logical section of my Traite de Zoologie. 2 For this reason it has 



1 XXXVIII 330. 



3 XLIII, 567, 624, 961, 1605, 2251, 2565. 



