Germinal Selection 37 
vary, they may grow and divide more or less rapidly, and their 
variations give rise to corresponding variations of the organ, cell, 
or cell-group which they determine. That they are undergoing 
ceaseless fluctuations in regard to size and quality seems to me the 
inevitable consequence of their unequal nutrition ; for although the 
germ-cell as a whole usually receives sufficient nutriment, minute 
fluctuations in the amount carried to different parts within the 
germ-plasm cannot fail to occur. 
Now, if a determinant, for instance of a sensory cell, receives for a 
considerable time more abundant nutriment than before, it will grow 
more rapidly—become bigger, and divide more quickly, and, later, 
when the id concerned develops into an embryo, this sensory cell will 
become stronger than in the parents, possibly even twice as strong. 
This is an instance of a hereditary individual variation, arising from 
the germ. 
The nutritive stream which, according to our hypothesis, favours 
the determinant NV by chance, that is, for reasons unknown to us, may 
remain strong for a considerable time, or may decrease again ; but 
even in the latter case it is conceivable that the ascending movement 
of the determinant may continue, because the strengthened deter- 
minant now actively nourishes itself more abundantly,—that is to say, 
it attracts the nutriment to itself, and to a certain extent withdraws 
it from its fellow-determinants. In this way, it may—as it seems to 
me—get into permanent upward movement, and attain a degree of 
strength from which there is no falling back. Then positive or 
negative selection sets in, favouring the variations which are ad- 
vantageous, setting aside those which are disadvantageous. 
In a similar manner a downward variation of the determinants 
may take place, if its progress be started by a diminished flow of 
nutriment. The determinants which are weakened by this diminished 
flow will have less affinity for attracting nutriment because of their 
diminished strength, and they will assimilate more feebly and grow 
more slowly, unless chance streams of nutriment help them to recover 
themselves. But, as will presently be shown, a change of direction 
cannot take place at every stage of the degenerative process. Ifa 
certain critical stage of downward progress be passed, even favourable 
conditions of food-supply will no longer suffice permanently to change 
the direction of the variation. Only two cases are conceivable; if the 
determinant corresponds to a useful organ, only its removal can bring 
back the germ-plasm to its former level ; therefore personal selection 
removes the id in question, with its determinants, from the germ- 
plasm, by causing the elimination of the individual in the struggle for 
existence. But there is another conceivable case ; the determinants 
concerned may be those of an organ which has become useless, and 
