A Systematic Study of the Anthomyiinab of New York 55 



radicum, and other species; or an invagination to form a flat, laterally 

 compressed, rudder-like plate, as in Hylemyia curvi'pes, H. hrassicae, 

 Pegomyia vanduzeei, P. luteola, P. winthemi, and other species. At the 

 lateral extremities of the basal rim, in the region of the cephalo ventral 

 angle of the ninth tergum, there sometimes arise arched chitinous lamellae 

 that extend in a complementary manner to the penis sheath, partially 

 or entirely encircling the caudal limits of the axial system of the penis; 

 for example, in Pegomyia hicolor, P. fuscofasciata, P. connexa, P. luteola, 

 Hylemyia variata, Paregle cinerella, and other species. 



The penis sheath, when present, arises from the basal rim as a thin, 

 arched plate, appearing like a cradle for the reception and protection of 

 the genital appendages when retracted, as in Hylemyia trichodadyla, H. 

 alcathoe, H. laevis, H. inornata, Pegomyia afinis, Hammomyia spp., and 

 other species. The distal margin of the sheath varies in contour, usually 

 protruding on each side to articulate with the lateral extremities of the 

 cephalic pair of internal lobes of the genital appendages. Frequently the 

 penis sheath is reduced to a thin, transverse, chitinous plate between the 

 arms formed by the basal rim. (Plate I, b and c.) 



The axial system of the penis 



The chitinous box. — The chitinous box is located as a central pivot for 

 the support and radiation of the other structures constituting the axial 

 system of the penis. It is in reality a hollow channel, which is surrounded 

 loosely by two convex chitinous plates and through which the ejaculatory 

 duct passes. In Pegojnyia luteola the box appears as a framework, with 

 arms of reinforced chitin for the support of the ejaculatory hood and the 

 caudal pair of internal lobes. (Plate I, a, b, and h.) 



The ejaculatory hood. — The ejaculatory hood typically arises as a tubular 

 process, in a median position on the dorsal surface of the chitinous box. 

 It stands erect by means of a thinly chitinized supporting membrane and 

 bears at its apex a small membranous swelling or inflation. In many 

 species (for example, Pegomyia luteola and Hylemyia trivittata), membranous 

 folds or " ears " are developed laterad. In Anthomyia pluvialis the folds 

 are large, and tend to obscure the central axis or process. In Pegomyia ruhi- 

 vora the ejaculatory hood appears slender and flexible, and is supported at 

 its base by a chitinous sheath of the chitinous box. (Plate I, a, b, and h.) 



The ejaculatory process. — The free, terminal appendage of the axial 

 system of the penis is the ejaculatory process. It arises in close apposition 

 to the caudal limits of the chitinous box, and continues the protective 

 channel for the ejaculatory duct which has been partially formed by the 

 chitinous box. In addition to this function, its purpose is to accentuate 

 and bear the genital aperture. This orifice may be supported by a cliiti- 

 nous ring or capsule, as in Pegomyia spp., Calythea albicincta, and Paregle 

 cinerella; or it may be surrounded by a frill of delicate, hyaline raembrane. 

 (Plate I, A, B, and i.) Both the shapes and the appearances of the ejaculatory 



