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.??° 
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 
Roux: Der Kampf der Teile im Organismus. P. 182. 
