2 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 
attempts to get them have been made. It nevertheless seemed desir- 
able to discover whether the kind of differences that distinguish wild 
species are also the kind that are appearing in the laboratory as muta- 
tions. This question will be discussed in detail later in this paper. 
An attempt has been made to bring together here the more important 
available information concerning the North American members of 
the tribe Drosophiline, and more especially the genus Drosophila. 
Exotic forms are discussed occasionally, but no extensive treatment 
of them has been possible. The data concerning the taxonomy, 
anatomy, development, distribution, and habits of the group are pre- 
sented as fully as available material will permit. Only a brief survey 
of the experimental work on the group has been attempted, but a 
bibliography of the experimental literature (with the more important 
papers on other lines) is presented. 
ACKNOWLEDGMENTS. 
This study has been made possible only by the favors and encourage- 
ment received from many different sources. It would not be possible 
to mention here all those who have helped in one way or another 
toward the completion of the undertaking. There are, however, 
several to whom my thanks are especially due. 
I have made extensive use of the collections and library of the 
American Museum of Natural History, and am under great obliga- 
tions to Dr. F. E. Lutz and Mr. A. J. Mutchler for the pains they have 
taken to facilitate this use. Professor J. M. Aldrich and the late 
Mr. Frederick Knab, at the United States National Museum, and 
Mr. C. W. Johnson, at the Museum of the Boston Natural History 
Society, have given me every facility for studying the material under 
their care. Extensive loans of material from these three museums have 
been of very great help. Through the kindness of Mr. Samuel Hen- 
shaw and of Mr. Nathan Banks I have been enabled to examine the 
Loew collection in the Museum of Comparative Zoology at Harvard. 
Loans of valuable material have been received from Mr. C. W. 
Johnson, Professor J. M. Aldrich, Professor A. L. Melander, and Mr. 
S. W. Frost. Dr. J. C. H. de Meijere has sent me several European 
species, properly named, and these have been very valuable for com- 
parison with American forms. Mr. C. G. Lamb has supplied valuable 
information concerning several exotic forms about which I was in 
doubt. 
Local collections of considerable interest have been sent to me by 
several people. The most significant of these are the following: 
Dr. O. L. Mohr, from Norway; Professor J. Arias, from Spain; Mr. W. 
S. Adkins, from Tennessee and elsewhere; Dr. R. R. Hyde, from 
Indiana and Maryland; Dr. F. Payne, from Indiana; Mr. D. E. 
Lancefield, from Oregon; Mr. C. T. Ramsden, from Cuba; Mr. L. L. 
