46 CHARLES W. METZ 



The object of this preUminary paper is to examine briefly the 

 chromosomes of several species belonging to the genus Drosophila. 

 This is a widely 'distributed genus and contains a large number of 

 species, of which the most common is the ordinary 'pomace fly' 

 or 'banana fly,' Drosophila ampelophila, already well known in 

 genetic circles from the experimental work of Morgan and his 

 students. Aside from D. ampelophila, about a dozen other species 

 have been reared in the laboratory and studied cytologically. In 

 the task of obtaining, breeding and identifying the flies I have 

 been greatly assisted by Mr. A. H. Sturtevant, who has shown an 

 active interest in the progress of the work from the beginning, 

 and has kindly furnished cultures of several species which could 

 not otherwise have been obtained. Some of the species studied 

 have apparently never been described by taxonomists, and there- 

 fore, cannot be referred to by name in this paper. Consequently 

 they are designated Species A, B, C, etc. 



Among the twelve different species examined five distinct 

 types of chromosome groups have been found,- each of which is 

 characteristic of one or more species. These types, when com- 

 pared with one another, chromosome by chromosome, show a re- 

 lationship, which, if the hypothesis outlined below be true, may 

 indicate an evolution of chromosomes in the genus. At all 

 events, there is here presented a .series of related chromosome 

 groups more complete than has been found in any other genus of 

 animals or plants known to me. 



Owing to peculiarities of the male Drosophila, it has been nec- 

 essary to take the data for this study principally from female 

 specimens. The males, unlike those of most insects, are much 

 less satisfactory for chromosome studies than the females, and 

 therefore have been reserved for separate treatment. The male 

 chromosome groups of two or three species are included, as men- 

 tioned in the text, but otherwise only the diploid female groups 

 are considered. The latter are sufficient for present purposes, 

 since only the normal somatic divisions are involved, and in these 



^ The chromosomes of one species, D. ampelophila, have been previously de- 

 scribed by Dr. Stevens, ('07, '08). 



