ON THE VITALISTIC VIEW OF NATURE. 461 



cated case seems to have been established. 1 On the other 

 side the influence of crossing, of the repeated division 

 and fusion of different germ-plasmas, to which Darwin 

 in his later writings attached more and more importance, 

 and on which Weismann relies exclusively for an ex- 

 planation of variation and natural selection, is denied 

 by some biologists to tend in the direction of the 

 gradual growth of definite characters : they point rather 

 to the obliterating and diluting influence of such pro- 

 miscuous fusion, and they maintain that the presence of 

 an environment which always acts in a constant manner 2 

 is indispensable. 



If we now look back for a moment on the funda- 

 mental change of ideas which the century has brought 

 about in the biological aspect of nature, we are bound 

 truly to halt in astonishment. In no department of 

 thought have comparatively small beginnings and de- 

 tailed discoveries, referring to infinitesimally small 

 phenomena, led to such revolutionary ideas concerning 

 those phenomena which most intimately affect our 

 personal interests the problems of life and death, of 

 conduct and of health. The whole of this change has 

 been brought about by introducing and extending those 



1 It is needless to give special 

 references, as all the recent works 

 on the subject, which have been 

 largely quoted in this chapter, deal 

 with this point. See, however, 

 Yves Delage, ' L'He're'diteY p. 196, 

 for a very complete bibliography. 

 He concludes as follows : " II n'est 

 pas demontre" que les modifications 

 acquises sous 1'influence des con- 

 ditions de vie soient ge"ne"ralement 



he're'ditaires, mais il parait bien 

 certain qu'elles le sont quelquefois. 

 Cela depend sans doute de leur 

 nature. D'ailleurs on ne sait pas 

 quelle est dans ce re"sultat la part 

 de la transmission des modifications 

 somatiques aux cellules germinales 

 et celle de 1'action directe des con- 

 ditions ambiantes sur celles-ci " (p. 

 221). 



2 Hertwig, ' The Cell,' p. 319. 



