54 H. C. HUCKETT 



to approximate caudad, whence they articulate v^-ith the basal process 

 of their respective dististyh. The basistyh articulate cephalad with the 

 lateral expansions of the basal rim of the. penis sheath, as in Pegomyia 

 rubivora, P. connexa, P. Irpsia, P. innthemi, P. luteola, and others, or 

 coalesce with and strengthen the mn itself, as in Hylemyio. ciUcnira, H. 

 antiqv.a, H. trichodadyla, Hydrophoria spp., Egle spp., and others fPlate I, 

 c). In Pegomyia juveriilis each basistylus seems to have divided longi- 

 tudinally into two, so that each rod ser^'es to connect an upper articulation 

 of the dististylus with the lower articulation of the basal rim of the penis 

 sheath, and a lower articulation of the dististylus "^-ith the upper articula- 

 tion of the basal rim of the penis sheath. 



The genital pouch 



The genital pouch is that region which forms the floor, or ventral sur- 

 face, of the hA-popygium, and over which the cerci and the dististyli 

 fold like the blade of a knife. The cephahc region of the pouch is boimded 

 by the semicircular, strap-like, sixth sterntmi. Situated in the pouch is 

 a group of small chitinous appendages, known as the penis ^oedagus), 

 which guide and direct the succes ful act of copulation. IMetcalf (1921), 

 in his excellent paper on the male genitalia of the SjTphidae, has fully 

 described and identified these appendages. The structures there shown 

 are in princ pie the same as those found m this subfamil}-, and ^Metcalf's 

 nomenclature has been followed. 



The penis, therefore may be divided into two systems as follows: 



I. The peripheral system: 

 a. The penis sheath. 

 II. The axial system: 



a. The chitinous box. 



b. The ejaculatorj' hood. 



c. The ejaculatorj- process. 



d. The sustentacular apodeme. 



e. The internal lobes: 



1. The caudal pair. 



2. The cephalic pair. 



The periphera' system of the penis 



The penis sheath. — The penis sheath is much reduced and is largeh' rep- 

 resented by the stout, hea^oly chitinized, basal rim, which appears as an 

 arched plate defining the cephalic limit of the axial sj'stem of the penis. 

 At its lateral extremities the rim supports the cephaloventral processes 

 of the ninth tergum, and thence it passes mesad to art culate with the 

 basistyh; or it is reinforced throughout the greater part of its extent by a 

 fusion with the basistyh. The basal rim is composed of two lateral p ces 

 which come to meet and ftLse cephalad n the mid ventral line. At this 

 point there frequently appears a prolongation of the cliitin along the mid- 

 ventral line, as in Pegomyia juvenilis, Hylemyia alcathoe, H. laevis, Paregle 



