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 suffi- 

 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." 19 



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- 



199 Delage : Ibid. P. 85485?. 



