598 



THE AMERICAN NATURALIST 



[Vol. L 



Type J 



Eepresented by 

 Drosophila obscura Fall. California and Oregon. 

 (Metz, '16, Figs. 41-50.) 

 Ovarian cells of B. obscura contain three rod-like eu- 

 chromosome pairs, one small w -chromosome pair and one 

 very long, V-shaped sex chromosome pair (diagram 

 J, ?). In the male the sex chromosomes are very dis- 

 similar, Y being straight and only about half as long as X. 



Type K 



Eepresented by 

 Drosophila affinis Sturtevant mss. Alabama. 

 (Metz, '16, Figs. 42 and 43.) 



In general this type resembles the last, but differs in 

 having two S-, or hook-shaped pairs in place of rod-like 

 ones. Apparently this peculiar shape is due to a sub- 

 terminal attachment to the spindle, although I have been 

 unable to get figures actually demonstrating the attach- 

 ment. In some cases one or both pairs extend radially 

 from the center of the figure as if they were attached 

 terminally, but usually their position is characteristically 

 that described above. In any event the two pairs are 

 readily distinguished from any others of the group, un- 

 like those of D. obscura. 



Type L 



Represented by 

 Drosophila caribea Sturtevant mss. Cuba, Panama. 

 (Figs. 19 and 20.) 



This type is radically different from any of those de- 

 scribed above, and like the two preceding is represented 

 by only one species. Female (ovarian) groups are com- 

 posed of four long Y-shaped pairs of chromosomes, one, 

 of which is shorter than the other three. In the male one 

 pair is conspicuously unequal, much as in types I, J and 

 K, but I have been unable to determine with certainty 

 whether this is the small pair or one of the large ones. 

 It is represented as a large one in the diagram (L, <$). 



