218 GENITALIA OF MALE DIPTERA AND MECOPTERA 



outgrowths of the ninth tergite, or the pseudo-styh ps of the 

 insect shown in figure 11, under the designation ''genitaha/' as 

 well. 



Metcalf, 1921, divides the abdomen of the Syrphidae (sensu 

 lato) into a pieal)domen and a postabdomen; the preabdomen 

 includes the segments which are not greatly modified (i. c. it 

 includes segment four of figure 23), while the postal)domen in- 

 cludes the reduced and modified segments (i.e. segments five to ten 

 inclusive, in figure 23) which are usually contorted or twisted 

 about in a peculiar fashion in adaptation to the method of mating 

 of these Diptera. The designations preabdomen and postal)- 

 domen are very convenient ones in syrphid morphology, but 

 are not applicable in most other insects, althought the slender 

 terminal segments of certain Mecoptera might readily be dis- 

 tinguished as the "postabdomen." The pecuHar twisting of 

 the terminal segments of male syrphids has already been referred 

 to. The condition met with in the syrphids, however, is quite 

 different from the torsion of the terminal segments (usually the 

 ninth — or eighth also — and the anus-bearing segments) in male 

 culicids, certain mycetophilids, etc. Unlike the torsion of the 

 genitalia of male sawflies, the anus-bearing segments are also 

 involved in the revolution of the genitalia of the Diptera. As 

 shown in figure 24, this revolution of the parts of the male 

 would facilitate the insertion of the intromittent organ ae into 

 the opening of ninth segment of the female. I have not been able 

 to observe the copulation of many Diptera in order to determine 

 what parts of the female have become adapted to the reception 

 of the genitalia of the male insect; but in the female mycet- 

 ophilid shown in figure 21, the styloreceptor, or plate labeled sr, 

 apparently is developed to receive the genital styles h of the 

 male shown in figure 24, although in many cases in these insects, 

 the claspers of the male slip backward and pinch the sternite 

 of the eighth segment with such force that it is surprising lliat 

 the female is not liurt by the pressure, the ('hTs])ers l)oiiig so 

 tensely pressed together that even plunging a coi)ulating i)air 

 into alcohol docs not cause the male to loosen his grasj) in most 

 instances. 



