112 CARNEGIE INSTITUTION OF WASHINGTON. 



taining, if possible, their genetic relationships. The failure of all attempts at 

 hydridizing species having different chromosome numbers has led to an ex- 

 tension of the intensive study of the selected individual species mentioned in 

 previous reports. The genetical analyses thus obtained are being compared 

 with one another and with that of the well-known Drosophila melanogaster 

 (am.pelophila) . 



"Studies on Drosophila virilis (a species possessing 6 pairs of chromosomes) 

 have resulted in the identification of 5 groups of linked genes, representing, 

 it is believed, the 5 large pairs of chromosomes. Approximately 30 genes are 

 represented in the 5 groups. The sex-linked group of characters in D. virilis 

 contains 3 members showing such a resemblance in morphological features 

 and genetical behavior to 3 in the sex-linked group of Drosophila melanogaster 

 as to suggest very strongly that they are homologous in the two species and, 

 consequently, that the sex-chromosomes of the two species are similar in 

 constitution. In the non-sex-linked or autosomal groups the evidence is 

 insufficient, as yet, to indicate whether or not similar homologies exist between 

 other chromosomes in the two species. 



"In Drosophila willistoni more than 40 mutant characters have been 

 studied — mainly by Mrs. Rebecca C. Lancefield. These characters fall 

 into three groups, corresponding to the number of large chromosomes. 

 Particular interest attaches to Drosophila willistoni because of the lack 

 of any conspicuous parallelism between its mutant characters and those of 

 any other species thus far studied. No explanation of this fact is apparent at 

 present, and a detailed discussion of the results may, therefore, be postponed 

 until further evidence is secured. 



"Our material of Drosophila obscura has been transferred to Mr. D. E. 

 Lancefield, of Columbia University, who has undertaken extensive work on 

 this species." 



STERILITY IN MUTANT HYBRIDS OF DROSOPHILA VIRILIS. 



Dr. Metz and Dr. Weinstein have discovered in Drosophila virilis 

 a series of 3 allelomorphic sex-linked mutations affecting the eye: 



(1) Rugose: Characterized somatically by a slight paling and rough- 

 ening of the eye, evident in the male only, the female being entirely 

 normal in appearance; in fertility both sexes seem to be fully equal to 

 the wild stock. 



(2) Glazed: This is more extreme in all respects; the eyes have a 

 glazed appearance in both sexes, though the males are the more 

 affected. Affected females are usually sterile. Of 150 females tested, 

 3 only were fertile. The males have a reduced fertility. 



(3) Wax: This is still more extreme. The eyes of both sexes are 

 greatly affected, resembling masses of yellow wax. The females seem 

 to be practically or entirely sterile. The males appear to breed more 

 poorly than do the glazed males; when rugose and glazed are crossed 

 the hybrid females are rugose-like, but are all sterile. When rugose 

 and wax are crossed, the hybrid females are all rugose-like but nearly 

 all are sterile. Hybrids from "rugose," ''glazed," or ''w^ax" mated 

 with other mutants are fertile. It appears, then, that the sterility of 

 ''glazed" and "wax" does not reappear in hybrids with more fertile mu- 

 tants except their allelomorph ''rugose." This sterility of certain 



