THE NORTH AMERICAN SPECIES OF 
DROSOPHILA. 
I. INTRODUCTION. 
Drosophila 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 Drosophiline, though many 
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