56 HEREDITY 



same change of nutrition. The difference between 

 male and female gametes is presumably a difference 

 of determinants, hence the difference in the reaction 

 of the male and female gametes is a difference of 

 reaction, not on the part of the cells as a whole, but 

 on the part of certain of their determinants — which is 

 precisely in accordance with Weismann's contention. 

 Other experiments demonstrated the existence of a 

 seasonal variation, showing that " inequalities of 

 nutrition" dependent on the time of year un- 

 doubtedly affect the sex-cells of the sea-urchin, 

 which are typical of germ-plasm in general. 



Various experiments of Cossar Ewart on the rabbit, 

 and of De Vries on plants, seem also to support the 

 view that the germ-plasm is affected by "inequali- 

 ties of nutrition." But, indeed, the assertion that 

 the germ-plasm, unlike all other living entities, is 

 not subject to change in virtue of its converse with 

 its environment, was quite incredible from the first. 



But, since we are consulting authorities, we will 

 do well to consider the conclusions reached by the 

 profoundest intellect — not even excepting Aristotle's 

 — that has ever been applied to the problems of 

 biology. In his " Principles of Biology," published 

 forty years ago, Herbert Spencer considered the 

 question of the origin of variations, and it goes 

 without saying that he did not content himself 

 with any such petitio ponncipii as is involved in 

 the assumption of an "inherent tendency to vary." 

 Spencer's discussion of the question follows closely 

 upon his setting forth of the great conception of 

 " physiological units," which now — under various 



