A DEFENCE OF MENDEL'S PRINCIPLES 



OF HEREDITY. 



" The, most fertile men of science have made blunders, and their 

 consciousness of such slips has been retribution enough; it is 

 only their more sterile critics who delight to dwell too often 

 and too long on such mistakes" BIOMETRIKA, 1901. 



INTRODUCTORY. 



ON the rediscovery and confirmation of Mendel's Law by 

 de Vries, Correns, and Tschermak two years ago, it became 

 clear to many naturalists, as it certainly is to me, that we 

 had found a principle which is destined to play a part in 

 the Study of Evolution comparable only with the achieve- 

 ment of Darwin that after the weary halt of forty years 

 we have at last begun to march. 



If we look back on the post-Darwinian period we 

 recognize one notable effort to advance. This effort 

 fruitful as it proved, memorable as it must ever be was 

 that made by Galton when he enuntiated his Law of 

 Ancestral Heredity, subsequently modified and restated 

 by Karl Pearson. Formulated after long and laborious 

 inquiry, this principle beyond question gives us an 

 expression including and denoting many phenomena in 

 which previously no regularity had been detected. But 



