176 APPENDIX. 



at the end of a large work of 800 pages. Darwin here 

 says (vol. ii., p. 349) : " I am aware that my view is 

 merely a provisional hypothesis or speculation ; but 

 until a better one be advanced, it will serve to bring 

 together a multitude of facts which are at present left 

 disconnected by any efficient cause." Weismann's 

 speculations, equally unfounded on fact, are never- 

 theless viewed by him as being of sufficient import- 

 ance to demand the most detailed elaboration. Do 

 not suppose for an instant that I am decrying the 

 use of fancy or provisional hypotheses ; the world 

 advances upon the steps, generally the ruined steps, 

 of hypotheses. The value of an hypothesis depends, 

 however, entirely upon whether we can put it to the 

 test of experiment. If it is intangible, then it re- 

 mains an hypothesis, while the great body of fact 

 workers go on building their sciences, and in the 

 completion of these it has no part. Darwin's pan- 

 genesis has no value as an hypothesis, it seems to me, 

 apart from its being a pictorial way of illustrating 

 how use and disuse might be inherited. This latter 

 is a question which can be solved experimentally; 

 pangenesis was a mental picture present to Darwin's 

 mind, and he threw it out for what it was worth. In 

 this picture the gemmules were supposed to pass 

 from the cells of the body through the blood into the 

 reproductive cells, and the experiments which Galton, 

 and subsequently Romanes, undertook to disprove 

 pangenesis by showing that certain samples of blood 

 did not contain gemmules, and that therefore pan- 

 genesis did not occur, appear to me to show a want 



