Delage 267 



lus in respect to the useless femur, already so atrophied, 

 have been greater in the former than in the latter? The 

 progressive diminution of the femur remains thus entirely 

 unexplained. 



Finally Delage accounts for the parallelism between 

 ontogeny and phylogeny in the following way: 



"The functional stimulus appears, we agree with 

 Roux, even in embryonal life, but is at this time certainly 

 weaker than after birth. There results from that a note- 

 worthy consequence which escaped Roux. That is that 

 at least the relative atrophy of the organ becomes more 

 marked the older the animal becomes, and that, in respect 

 to the atrophied organ, the young, and above all the 

 embryo, must differ much less from the ancestral forms. 

 Thus there is explained at once the parallelism between 

 ontogeny and phylogeny in everything which is depend- 

 ent upon atrophy or hypertrophy induced by use or dis- 

 use, that is in very many cases." 20 



Is it inactivity that really causes in serpents the retro- 

 gression during embryonal life of the already partially 

 developed limbs? Or is it use that in the salamanders 

 causes to any extent the development, during embryonal 

 life, of the same limbs? Whence come these very unlike 

 embryonal processes of activity or inactivity? Why did 

 not this same inactivity, consequently this same atrophy, 

 show itself in the embryos of the remote ancestors of 

 the serpents of today? Why does the inactivity and 

 consequently the atrophy of these extremities depend, 

 in the egg of the present day serpents, upon conditions 

 within the embryonic organism itself, and manifest itself 

 at exactly that ontogenetic moment, which corresponds 



200 Delage : Ibid. P. 856857. 



