No. 598] CHROMOSOME STUDIES ON THE DIPT ERA 593 



In D. amocita and S. ?/ ram i >/ h in spermatogonia! figures 

 indicate that X and Y are unequal and straight ( Kig. 5. 

 and Metz, '14, Figs. 2 and 3); while in D. bus, L i!, I), 

 flora, D. bromelia:, D. robust a and J), lint bat a no in- 

 equality is evident. The other species have not been 

 examined with respect to spermatogonial groups. In D. 

 robusta the rod-like members (sex chromosomes?) ap- 

 pear to be hook-shaped and to be attached sub-terminally 

 to the spindle in much the same manner as the F-chromo 

 some in ampelophila. 



Another modification or sub-type is represented by I), 

 flora and D. bromelia, in which the ///-chromosomes are 

 materially larger than in the other species. Indeed, those 

 of the former are so large as to suggest a transition be- 

 tween m-chromosomes and /•-chromosomes. 



Type B 



Represented by 

 Drosophila earlei Sturtevant mss. Cuba. (Figs. 

 6-9.) 



This interesting type consists of one short rod-like pair 

 and two large V-shaped pairs, one of which is much 

 longer than the other. No trace of m-chromosomes has 

 thus far been found in the fifteen or twenty figures I have 

 studied. Unfortunately I have not yet secured good 

 spermatogonial figures and am unable to identify the sex 

 chromosomes. 



In many respects type B is of greater interest than any 

 other type of chromosome group I have studied, for it not 

 only contains the smallest number of chromosomes tlms 

 far found among the higher flies, 5 but each of its three 

 pairs is conspicuously different from either of the other 

 two, making possible an individual identification of the 

 chromosomes not obtainable, with such a degree of cer- 

 tainty, in any other known species of Diptera. If a 

 genetic continuity of chromosomes be admitted there can 

 be no question that here each paternal chromosome as- 



