266 Theories Treating of Inheritance 
of centuries ago, whose femur was only a very little 
greater than that of the whales of today.” 
It still remains then to explain, without devising 
some improbable hypothesis, how the same kind of egg 
can produce two different forms. And that is not very 
difficult when one keeps functional excitation in mind.” 
“When an animal has a femur 20 cm. long, that 
does not indicate that in its egg all the conditions were 
present for the formation of a bone of this length. That 
indicates only that the elements necessary for it are 
there, which with the co-operation of the functional 
stimulus can form a femur of such length. We cannot 
know just what part this latter takes in the result, but 
it must be considerable.” 
“While the whale had still a femur, which though 
not normal was yet only half atrophied, the femur pro- 
ducing factors inherent in the egg were perhaps suffh- 
cient to produce a bone of only the size of that present 
in the whales of today, and the functional stimulus, 
which as Roux has shown, begins to operate even in 
embryonal life, did the rest. It is therefore not astonish- 
ing that upon the cessation of the functional stimulus, the 
femur became reduced to a very little rudiment.” 1° 
But the embryonal functional stimulus in the whales 
of many centuries ago whose femurs were only a very 
little bigger than those of the whales of today, cannot have 
been different from the embryonal functional stimulus 
of the whales of today, no matter how much one may 
limit direct morphological action of the egg, if one starts 
out from the hypothesis that the eggs concerned are quite 
identical. Why should the embryonal functional stimu- 
Delage: Ibid. P. 854—857. 
