II 



On the Bearing of Mendelian Principles of 



Heredity on Current Theories of the 



Origin of Species 



(Manchester Memoirs, Vol. xlviii., 1904, No. 24) 



A WIDE field of work and speculation has been opened up 

 to the student of evolution by Mendel ; and by his fol- 

 lowers it has been maintained that it is only by working 

 on the lines laid down by the Abbot of Briinn that a solu- 

 tion of the problem of the origin of species can ultimately 

 be reached. It is the object of this paper to show the rela 

 tion which Mendel's work bears to current theories of organic 

 evolution. 



(1) On the Difference between Continuous and Dis- 

 continuous Variation 



For an account of continuous variation the reader is 

 referred to the Presidential Address to Section D of the 

 British Association, at the Bristol Meeting, by Professor 

 Weldon (Weldon, '98) ^ : discontinuous variation is set forth 

 by Mr. Bateson in his work " Materials for the Study of 

 Variation " (Bateson, '99) ; all that remains for me to do 

 is to call attention to some of the differences between these 

 two conceptions of variation. 



Continuous variation is the name of a phenomenon of 

 everyday observation, namely, the fact that no two indi- 

 viduals of a species (plant or animal) are ahke ; it is a 

 permanent quality of all animals and plants at all times, 

 tending, as far as we can see, in any direction (and as little 



*, J'ide List of AuthoritieB, p. 139 infra. 



127 



