238 



THE AMERICAN NATURALIST 



[Vol. LVI 



8. The comparative lengths of the X-chromosome 

 maps in melanogaster and ivilUstoni suggests that there 

 is less crossing over in the latter than in the former. 



TABLE I 



In Tables II-VI parentheses indicate data omitted 

 from the regional summary on account of poor viability 

 of one class or else inability to classify one class. The 

 two columns under the respective headings represent 

 complementary classes, the one to the left that includ- 



