234 DANIEL UOSKN 



between these genes depends upon this circumstance. However, 

 according to the writer, the assumption may be made that the distance 

 between contiguous genes always remains the same, and that they 

 are more or less loosely combined on account of different degrees of 

 affinity. The different percentages of crossing over obtained may be 

 due to differences in degree of affinity between the different gênes. 



LITERATURE CITED. 



1. Castle, W. E. 1919. Is the arrangement of the genes in the chromosome 



linear? — Proceed. Nat. Acad, of Sciences 5. 



2. Federley, H. 1913. Das Verhalten der Chromosomen bei der Spermatogenese 



der SchmetterUnge Pygcera anachoreta, ciirtula und pigra sowie einiger 

 ihrer Bastarde. — Zeitschr. f. indukt. Abslamm. u. Vererbungslehre. Bd IX. 



3. Goldschmidt, R. 1917. Crossing over ohne Chiasmatypie? — Genetics 2. 



4. Morgan, Th. H. 1921. Die stoffliche Grundlage der Vererbung. Deutsche 



Ausgabe von H. Nachtsheim. Berlin. 



5. Morgan, Th. H., Sturtevant, A, H. and Bridges, C. B. 1920. The evidence 



for the linear order of the genes. — Proceed. Nat. Acad, of Sciences 6. 



6. Sturtevant, A. H. 1917. Crossing over without chiasmatype? — Genetics 2. 



7. Sturtevant, A. H., Bridges, C. B. and Morgan, Th. H. 1919. The spatial 



relations of genes. — Proceed. Nat. Acad, of Sciences 5. 



8. Weinstein, A. 1918. Coincidence of crossing over in Drosophila melanogaster. 



— Genetics 3. 



