52 H. C. HUCKETT 



THE MORPHOLOGY OF THE GENITALIA 



In order to prevent a possible misdetermination of the species of the sub- 

 fam ly Anthomyiinae, especially of its more closely related forms, and 

 to make clear those distinctions by which the species or specimens dis- 

 cussed in this paper can be recognized, it seems advisable to illustrate 

 certain characteristics of the male and the female genital organs and of 

 the fifth abdominal sternum of the male. This is done in the following 

 brief explanation of the anatomy of the male copulatory appendages and 

 of the ovipositor, the remarks being based on the structure of those parts 

 as they appear in Hy'emyia cilicrura Rond. 



MALE COPULATORY APPENDAGES 



The male copulatory appendages may be divided arbitrarily into four 

 groups, as follows: (1) the cerci, (2) the genital styles (gonostyh), (3) the 

 genital pouch (in which the genital appendages are situated), and (4) the 

 processes of the fifth abdominal sternum. 



The cerci 



The cerci $ens lato (forceps superiores) represent the paired appendages 

 of the atrophied eleventh segment. They appear typically as flattened 

 plates caudad of the anus and between the bases of the dististyli (forceps 

 inferiores). Morphologists are still uncertain whether these fused plates 

 represent the true limbs or rami of the appendages of the eleventh segment 

 — that is, the cerci sens strat. — or merely the basal plates or paraprocts 

 of such appendages. Such plates are always closely associated with one 

 another, whether completely fused along the mid line into one immovable 

 piece — as, for example, in Hylemyia cilicrura, Hammomyia spp., Hydro- 

 phoria spp., and others — or remaining semi-detached as two interdependent 

 plates, as in Pegomyia calyptrata, P. fuscofasciata, P. bicolor, Eustalomyia 

 spp., and others. 



Each cercus becomes closely associated with its respective dististylus, 

 whether by direct fusion in thin chitinous sheets or by an articulatory 

 mechanism in which a projection of the cercus fits into the complementary 

 socket of the dististylus beneath (Plate I, c). The shape of the cerci, 

 where seen from above, is of considerable taxonomic importance; their 

 forms are so diversified, and, in the more important specimens, so indescrib- 

 able, that only illustrations can satisfactorily indicate the significant 

 characters. In certain cases the cerci possess accessory characters, such 

 as the horn-like apical processes of Hylemyia trivittata, or the prong-like 

 structures of H. hetarum, H. inornata, H. setigera, and others. The arma- 

 ture of the cerci is invariably composed of bristles, setae, and hairs, 

 arranged in various ways. The bristles arranged along the margin of the 

 cerci are usually the stronger and longer; those on the inner areas are 



