1921] Metcalf: Genitalia of Male Syrphide Lit 
families are all ones in which little or no color differentiation is 
available for use. Hence, it has been particularly interesting in 
this family of large, brilliantly-marked flies to see how color 
markings would stand the acid test of comparison with really 
tangible structural features. 
So far as the Syrphide are concerned, only scattered ref- 
erences to the genitalia are to be found. Verrall* observed that 
the parts are unsymmetrically twisted to the right and, in sev- 
eral cases (e. g., Spherophoria and Tropidia), he gave super- 
ficial drawings of the parts. Walter Wesché’ makes frequent ref- 
erence to the condition of the parts in the Syrphide and gives 
figures of three species. Berlese! has given an excellent figure of 
the genitalia of Eristalis tenax. J. Herve-Bazin, in his treatment 
of the Syrphide of the Congo’, makes occasional reference to 
the exposed parts, but gives no description of the concealed 
parts. Lundbeck® gives especially valuable observations upon 
the condition of the segments of the postabdomen and remarks 
upon the appendages of certain species, but I feel sure that 
neither he nor Verrall had ever seen a cleared specimen and had 
little intimation of the valuable characters to be drawn from 
these parts. 
SCOPE AND AIM. 
In the present investigation the genitalia of only the male 
sex have been studied. The aim has been to determine the 
general character of the genitalia for this family, for the various 
genera, and for the several species; primarily as a help in lm- 
iting and clearly defining species and in fixing the limits of 
many of the genera now hopelessly intergrading and admittedly 
unsatisfactory. Furthermore, in these characters have been 
found some evidence regarding the phylogeny of the family 
and some good sub-family or tribe characters. The present 
paper is intended as an introduction to a series of taxonomic 
papers based on genitalic characters that are now prepared and 
in preparation and it is hoped also that it may serve as an intro- 
duction to this method of study for other specialists on this 
family. The writer must confess that his interest has been pri- 
marily taxonomic and that he has been least of all concerned in 
the much-mooted question of homologies and nomenclature 
of parts. 
