212 Inheritance of Acquired Characters 
deprived of his last stronghold saw himself forced to 
give an explanation for these co-ordinated variations 
also, which should prove, at least from a theoretical 
point of view, that they also might possibly be produced 
through natural selection. But it is just in this attempted 
explanation that he has fallen into the most evident 
contradiction, a thing which was inevitable anyway seeing 
that his thesis is untenable. It is worth while to spend 
a little more time examining this contradiction. 
He utilizes for this purpose a theory which, though 
introduced only at the last to supplement or replace the 
earlier, already discussed theories of panmyxia and the 
economy of the organism, was originally intended to 
give if possible some better explanation than the earlier 
theories offered of the continuous regression of useless 
organs even after any further regression is of no more 
value for natural selection. According to this theory 
when once the involutive process has begun in a given 
organ from any external provocation whatever, it would 
acquire in this very way an intrinsic tendency to bring 
about more and more retrogression. And the tendency 
acquired by this organ and now inherent in it toward 
constant phylogenetic regression would be accounted for 
by the following consideration. 
Weismann affirms that when the tendency to degen- 
erate once appears in an organ especially well developed, 
let us suppose by natural selection, that proves that it 
is represented from that time on in the germ plasm by 
determinants “of smaller growing power.” ‘But since,” 
he continues, “growth and assimilation are physiologic 
functions, just as are contraction and secretion, so the 
fundamental principle of intraselection is applicable to 
them: the functional stimulus strengthens the function- 
