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.” 2°? 
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 
20Delage: Ibid. P. 856—857. 
