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THE AMERICAN NATURALIST [Vol. L 



Drosophila flora; Sturtevant mss. Cuba. (Fig. 2.) 

 Drosophila limbata Will. Cuba. (Metz, '16, Figs. 

 10-12. 



Drosophila procnemis Will. Cuba. (Metz, '16, 



Drosophila quinaria Loew. New York. (Metz, '14, 

 Fig. 7.) 



Drosophila robusta Sturtevant mss. New York. 

 (Figs. 3 and 4; Metz, '16, Figs. 7-9.) 



Drosophila saltans Sturtevant mss. Cuba. 



Drosophila pallida Will. Cuba. 



Scaptomyza graminum Fall. New York. (Fig. 5; 

 Metz, '16, Figs. 4-6.) 

 This is type I of my previous paper, and is the prevail- 

 ing type among the species studied, being represented by 

 thirteen of the total twenty-nine. It consists of two pairs 

 of long, Y-shaped chromosomes, one pair of straight sex 

 chromosomes, and one pair of m-chromosomes. 



Slight modifications of this type are found in certain 

 species, usually characterized by peculiarities in the sex 

 chromosome pair. In D. ampelophila it appears from 

 the work of Bridges ( '16) that the J-chromosome, instead 

 of being straight as is the X-chromosome, is hook-shaped 

 or Y-shaped, although never large enough to be confused 

 with the Y-shaped euchromosomes. My observations 

 confirm those of Bridges in this regard with the exception 

 of two figures in which X and Y appear equal and 

 straight. Perhaps these are due to accident, but they are 

 entire figures and normal in other respects. 



