THE NORTH AMERICAN SPECIES OF 



DROSOPHILA. 



I. INTRODUCTION. 



DrosopMla melanogaster Meigen {ampelophila Loew) has in recent 

 years come to be widely used as a laboratory animal, especially in the 

 study of heredity. Its short life-cycle, great productivity, and the 

 ease with which it may be bred have been chiefly responsible for making 

 it so popular for this purpose. These small flies have been used not 

 only in the study of genetics, but also in investigations dealing with 

 cytology, behavior, and various phases of physiology. It has also been 

 found that several other members of the same group are amenable to 

 laboratory life, and these species offer numerous additional possibili- 

 ties for interesting experimental work, which are now beginning to be 

 exploited. 



In view of these facts, it has seemed to the writer that a systematic 

 review of the group would be desirable. No comprehensive study of 

 the American forms has hitherto been made, so that our knowledge of 

 the number of species and of their distribution and habits is very 

 fragmentary. Furthermore, much of the published data on these 

 points is unreliable, for the reason that different names have sometimes 

 been applied to the same form, or different forms have been given the 

 same name. Even when material has been identified by the same 

 entomologist, there is a large possibility of inconsistency — and this 

 applies to the writer's own determinations, for it is very easy to go 

 astray when identifying pinned material. It is hoped, however, that a 

 beginning has been made in the undertaking of bringing order out of 

 something very like chaos. 



There was another, somewhat different, reason for making a sys- 

 tematic study of the group. There has been a very large number of 

 mutations discovered in the laboratory races of Drosophila melano- 

 gaster Meigen, and also of other species, particularly of D. virilis 

 Sturtevant. It seemed to the writer that it would be of considerable 

 interest to get an idea of how these mutations compare with the differ- 

 ences between wild species of Drosophila. The comparison is difficult 

 to make without crossing species and comparing the inheritance of 

 mutations with that of specific differences. But fertile species hybrids 

 have so far not been obtained in the Drosophilinse, though many 



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