28U 



THE AMERICAN NATURALIST 



[Vol. XLIII 



of the individuals, the result would probably be utter con- 

 fusion instead of orderly development. We might as- 

 sume that albinism is dependent upon the peculiar prop- 

 erties of a single chromosome, that length of hair is de- 

 pendent upon the constitution of a second chromosome, 

 that a short tail is associated with a third, and so on. 

 These characters may not be represented by any kind 

 of structural element; they may have their basis in the 

 general chemical constitution of the chromosome and be 

 produced during development in a purely epigenetic 

 fashion. Chromosomes probably have their individual 

 peculiarities of chemical constitution as might be expected 

 from the fact that the chromatin content of an individual 

 represents contributions from many different ancestors. 

 Each chromosome or even a small constituent of the chro- 

 mosome may have a relation to the inheritance of the 

 whole body, but the peculiarities of one chromatic element 

 may dominate in one part, those of another chromatic ele- 

 ment in another. When albinism is eliminated it does not 

 mean that this character alone is separated, but the anlage 

 of an albino organism. Even if it is shown that the num- 

 ber of separate characters which Mendelize is greater than 

 the number of chromosomes of the variety, Mendelian 

 phenomena can be explained on the basis of sorting out 

 ancestral tendencies as wholes instead of unit characters. 

 The facts of Mendelian inheritance at present known do 

 not necessarily give any support to the theory of discrete 

 bearers of unit characters, or the theory of the inde- 

 pendent variability of parts as conceived by De Vries and 

 Weismann. This is a point which, I believe, needs to be 

 emphasized on account of the uncritical acceptance of 

 these views by so many writers on heredity and variation. 

 The presence or absence of certain characters may be 

 independent of the presence or absence of certain others, 

 but this fact may very readily be accounted for without 

 having recourse to a particulate theory of inheritance. 



The mixing up and separation of characters in inherit- 

 ance, far from proving the independent variability of 



