1921] Metcalf: Genitalia of Male Syrphide 173 
Mr. R. S. Sherman, of Vancouver, British Columbia; 
Major W. S. Patton, of Somerset, England; 
Prof. Charles T. Brues, of the Bussey Institution; 
Prof: R. A. Cooley, of the Montana Experiment Station; 
Prof. W. A. Riley, of the University of Minnesota; 
Prof. James S. Hine, of Ohio State University; 
Dr. J. Chester Bradley, of Cornell University; 
Prof. W. C. O’Kane, of New Hampshire Agricultural College; 
Prof. R. W. Doane, of Leland Stanford Junior University; 
Prof. S. J. Hunter, of the University of Kansas; 
Dr. W. M. Wheeler, of the Bussey Institution; 
Mr. A. W. Morrill, of the Arizona Agricultural College. 
To the members of the faculty of the Bussey Institution, 
especially Dr. W. M. Wheeler and Prof. Charles T. Brues, my 
thanks are due for the excellent facilities furnished for the 
major part of this work, for the generous loan of literature from 
their personal libraries and for many helpful suggestions. And 
finally it gives me pleasure to record the extensive and unselfish 
aid given me by my wife with many different phases of the 
work. 
ILLUSTRATIONS. 
The drawings have been made with several objects in mind: 
first of all, to exhibit the characteristic structures which may 
be used again and again by taxonomists in determining the 
species; but also to record the morphological structure of the 
parts, even those which are obscure, in order that homologies 
might be traced throughout this group and eventually with 
other families and even the other orders; and finally not with- 
out some joy in presenting the intricate and often artistically 
beautiful structures which Nature has here hidden from the 
cursory observer. 
Hence, much more extensive drawings have been made than 
would be necessary to illustrate the points needed 1n taxonomy; 
the characteristic structures are not unduly emphasized in the 
figures, although they are pointed out in the text; and no uni- 
form position, such as strictly dorsal or strictly lateral, has been 
regularly chosen for the views presented. The attempt has been 
made to place the parts in the position which would show the 
characteristic features to good advantage and also give, so far 
as possible, an ensemble of all the structures present. Most often 
this has been a ventral or cephalic view; although the lateral 
