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 Avhole usually receives sufficient nutriment, minute 

 fluctuations in the amount carried to different parts Mithin 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 Mill gi-ow 

 more rapidly — become bigger, and divide more quickly, and, later, 

 when the id concerned develops into an embryo, this sensory cell will 

 btKiome stronger than in the parents, possibly even twice as strong. 

 Tills is an instance of a hereditary individual variation, arising from 

 the germ. 



The nutritive stream which, according to our h;\'pothesis, favours 

 the determinant Nhy cliance, that is, for reasons unkno^vn 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 iqncard movement, and attain a degree of 

 strength from ivhich there is no falling hacJc. 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 donmward 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. If a 

 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- 

 plaam, 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 oigan which has become iiseless, and 



