234 EVOLUTION 



Sex," outlined in scattered papers and lec- 

 ture syllabuses, and with its beginnings 

 compressed into a too dry abstract at the 

 close of the old "Britannica" article "Varia- 

 tion and Selection," many years ago. 



Let us start from the acceptedly known, 

 from Darwin's natural selection, and this of 

 "indefinite" variations, and express the prob- 

 lem before us in the words of Weismann: 

 "We certainly cannot remain at the purely 

 empirical conception of variability and hered- 

 ity as laid down by Darwin in his admirable 

 work. In the first enthusiasm over the newly 

 discovered principle of selection, the one 

 factor of transformation contained in this 

 principle has been unduly pushed into the 

 background to make way for the other more 

 apparent and better known factors. The 

 first indispensable factor, and perhaps the 

 most important in any case, in every trans- 

 formation is the physical nature of the organ- 

 ism itself." 



This inquiry into the organismal springs 

 of variation must lead us far. For Weismann 

 these have led especially into his subtle 

 studies of the germ-plasm; but obviously 

 also they involve a fresh survey of the leading 

 types of variation as we see them developed 

 by plant and animal forms. Naturalists are 

 no longer so much setting out from the anal- 



