THE 



AMERICAN NATURALIST 



Vol. XLIV August, 1.910 No. 524 



CHBOMOSOMES AND HEREDITY 

 PROFESSOR T. H. MORGAN 

 Columbia University 



The Individuality of the Chromosomes 

 We have come to look upon the problem of heredity 

 as identical with the problem of development. The word 

 heredity stands for those properties of the germ-cells 

 that find their expression in the developing and de- 

 veloped organism. When we speak of the transmission 

 of characters from parent to offspring, we are speaking 

 metaphorically; for we now realize that it is not charac- 

 ters that are transmitted to the child from the body of 

 the parent, but that the parent carries over the material 

 common to both parent and offspring. This point of 

 view is so generally accepted to-day that I hesitate to re- 

 state it. It will serve at least to show that in what I am 

 about to say regarding heredity and the germ-cells I shall 

 ignore entirely the possibility that characters first ac- 

 quired by the body are transmitted to the germ. Were 

 there sufficient evidence to establish this view, our prob- 

 lem would be affected in so far as that we should not 

 only have to account for the way in which the fertilized 

 egg produces the characters of the adult, but also for the 

 way in which the characters of the adult modify the 

 germ-cells. 



The modern literature of development and heredity is 

 permeated through and through by two contending or 

 contrasting views as to how the germ produces the char- 

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