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 DrosophilinsB, though many

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