306 Explanation of Inheritance 



not been this pathological absence of this latter, the 

 ontogenetic stimulus and the functional would have co- 

 operated at the same time in the same formation. There- 

 fore one cannot, as we have said, be oblivious of the 

 indication that this harmonious and parallel co-operation 

 of the two stimuli, in combination with the fact that in 

 no embryonic structure whatever is there to be demon- 

 strated any substantial difference in the manner of forma- 

 tion and development between the purely hereditary 

 portion due to the ontogenetic stimulus alone, and the 

 portion due to the functional stimulus, is strongly in 

 favor of the essentially identical nature of these two 

 stimuli. 



Finally a number of organs which would attain their 

 complete development through the ontogenetic stimulus 

 alone, have their development hastened by the accidental 

 intervention before the proper time of the requisite 

 functional stimulus. Thus, for example, in prematurely 

 born children the visual sense develops earlier; that is to 

 say its development is accomplished in a total number of 

 days, counting 'from the first instant of development, that 

 is smaller than the ordinary number such as would be 

 given by the time of ordinary gestation augmented by 

 the number of days necessary for the infant born at term 

 to acquire the same degree of development of sight. 225 

 And this demonstrates again, that the functional stimulus 

 can replace the ontogenetic stimulus, or better, that it can 

 co-operate with it and add itself to it, thus strengthening 

 its effect; a thing which would be difficult to conceive of 

 were the two stimuli of different nature. 



To these facts of the most general character, we can 



22B Roux : Der Kampf der Teile im Organismus. P. 182. 



