172 Annals Entomological Society of America [Vol. XIV, 
ACKNOWLEDGMENTS. 
Nearly ten years ago, in a letter commenting upon my work 
with the biology of the Syrphidez, Dr. Raymond C. Osburn, then 
of New York City, made the following suggestion: 
“Tf you can secure the material, the study of the development of the genitalia 
in the pupa would be most interesting, as nothing has been done on that point in the 
Syrphide.”’ 
However, it seemed most expedient to determine first the 
actual condition of the parts in the adult before attempting the 
more difficult task of elucidating their embryonic development. 
Ever since that time I have had in mind an investigation of the 
hidden treasure of characteristics to be found in the male gen- 
italia of these flies. Occasional specimens have been examined 
from time to time, but it was not until 1918-19 that an oppor- 
tunity was afforded for a comprehensive study of the problem. 
The writer acknowledges with gratitude the early suggestion of 
the problem and also the interest shown in its solution and 
fruition by Doctor Osburn since he and the writer became 
associated in the same department. 
A paper such as this, the value of which depends funda- 
mentally on the correct identification of the materials used, 
and which requires a large series of specimens and species, is 
not possible without much aid and assistance from fellow 
workers. I feel that I have been unusually fortunate in this 
respect, for in almost every case the material desired has been 
given with the utmost generosity. 
Much of the material studied is from my own collection. 
This has been supplemented in many cases by specimens from 
other collections and determined by other workers. In a num- 
ber of cases I have been fortunate in securing type material. 
All of the important American genera and most of the minor 
ones have been studied, about sixty in all, represented by 
about two hundred species. To attempt a detailed statement of 
the materials loaned to me would require too much space; but 
I wish to express my gratitude for such aid to the following 
gentlemen: 
Dr. R. C. Osburn, of Ohio State University; 
Mr. Charles W. Johnson, of the Boston Society of Natural History; 
Mr. J. M. Aldrich, of the United States National Museum; 
Mr. Nathan Banks, of the Museum of Comparative Zoology, Cambridge; 
