Manchester Memoirs, Vol. xlviii. (1904), No. ^4. 



XXIV. On the Bearing of Mendelian Principles of 

 Heredity on current theories of the Origin of 

 Species. 



By A. D. Darbishire, B.A., 



Demonstrator of Zoology in the Victoria University of Manchester. 

 Received and Read March i^th, 1^04. 



A wide field of work and speculation has been 

 opened up to the student of evolution by Mendel : and 

 by his followers it has been maintained that it is only by 

 working on the lines laid down by the Abbot of Brtinn 

 that a solution of the problem of the origin of species can 

 ultimately be reached. It is the object of this paper to 

 show the relation which Mendel's work bears to current 

 theories of organic evolution. 



(i) On the difference between continuous and 

 discontinuous 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 

 individuals of a species (plant or animal) are alike ; 

 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 teleological in any sense of the word as 



July nth, igo4. 



