No. 631] FACTORS OF HEREDITY 121 



ideas of a spatial, physical linear arrangement, their in- 

 terpretation on the latter basis being natural and obvious. 



The idea that the genes are bound together in line, in 

 order of their linkage, by material, solid connections 

 thus remains as the only interpretation which fits the 

 genetic findings. In view of the additional fact that the 

 chromosomes— themselves known to be specifically linked 

 to the factor groups— can, at certain stages of their his- 

 tory, be seen to have the linear structure required, it 

 Would indeed be rash to adopt a different theory, with- 

 out most cogent evidence of a startlingly new character. 



1919. Is the Arrangement of the Genes in the Chromosome Lineal 



Proc. Nat. Acad. Sc., V, 25-32. 

 1919. The Linkage System of Eight Sex-linked Characters of Vrosi 

 pWa virilis. Proc. Nat. Acad. Sc., V, 32-36. 

 tz, C. W., and Bridges,' C. B. 



1917. Incompatibility of Mutant Races in Drosophila. Proc. Na, 



Acad. Sc., Ill, 673-678. 



tz, C. W. 



1918. The Linkage of Eight Sex-linked Characters in Drosophil 



virilis. Genetics, III, 107-134. 

 rgan, T. H., and Bridges, C. B. 

 1916. Sex-linked Inheritance in Drosophila. Carnegie Institution o 



Washington Publ. 237, 88 pp. 

 rgan, T. H., Sturtevant, A. H., Muller, H. J., and Bridges, C. B. 



1915. The Mechanism of Mendelian Heredity. 262 pp. Henry Holt 



1916. The Mechanism of Crossing Over. Amer. Nat., I, 193-221 



Zeitschr. 

 1918.' Coincidenc 



