The 



Journal of Heredity 



(Formerly the American Breeders' Magazine) 



Vol. X, No. 9 December, 1919 



CONTENTS 



A year ago the American Genetic Association announced its desire to com- 

 municate with twins living in any part of the world. The response has been 

 highly gratifying. Six hundred twins, and parents of twins, have written let- 

 ters, and approximately 175 photographs were received. This entire number 

 of the Journal is devoted to discussions based on this correspondence. 



Twins, by David Fairchild 387 



Resemblance and Difference in Twins, by C. H, Danforth 399 



Physical Correspondence in Two Sets of Duplicate Twins, by Harris 



Hawthorne Wilder 410 



Carriers of the Germ Plasm 422 



Twins Prove The Importance of Chromosomes, by Frederick Adams 



Woods 423 



Definition of Heredity — "Nature vs. Nurture" Not a Good Expression, 



bv Frederick Adams Woods 426 



The Journal of Heredity is published monthly with the exception of July, August 

 and September by the American Genetic Association (formerly called the American 

 Breeders' Association) for the benefit of its members. Canadian members who desire 

 to receive it should send 25 cents a year, in addition to their regular membership 

 dues of $2, because of additional postage on the magazine; foreign members pay 50 

 cents extra for the same reason. Subscription price to non-members, $2.00 a year, 

 foreign postage extra; price of single copies, 25 cents. 



Entered as second-class matter February 24, 1915, at the postoffice at Washing- 

 ton, p. C, under the act of August 24, 1912. Contents copyrighted 1919 by the 

 American Genetic Association. Reproduction of articles or parts of articles per- 

 mitted provided proper credit is given to author and to the Journal of Heredity 

 (Organ of the American Genetic Association), Washington, D. C. 



Date of issue of this number, DEcember 24, 1919. 



