194 Annals Entomological Society of America [Vol. XIV, 
The parts of each system will now be considered as follows: I, The 
axial system: a, the ejaculatory process; 6, the chitinous box; c, the 
ejaculatory hood; d, the internal lobes; e, the sustentacular apodeme; 
f, the ejaculatory sac and g, the ejaculatory apodeme. II, The peripheral 
system: h, the penis sheath and its basal rim; 7, the cephalic emargina- 
tion; 7, the lingula; k, the superior lobes and /, the inferior lobes. 
A. THE AXIAL SYSTEM OF THE PENIS. 
The terminal continuation of the ejaculatory duct, called the 
ejaculatory process, and the associated structures present a surprising. 
variation in the different genera and even in very closely related species. 
All these parts are evidently in a process of rapid evolution and hence 
afford excellent specific characters, but yield a very meager amount of 
data as to phylogeny of groups. The entire known range of variation 
may be found almost in a single genus. 
(a). THe Eyacutatory Process: The orifice of the duct, one of 
the important landmarks, is often difficult to locate. It varies from 
a very minute aperture (Chrysogaster, Mesogramma, Helophilus, Crior- 
hina, Microdon, etc., Figs 37, 38, 41, Plate X; 86, 91, Plate XVI; 97, 
129: 130) Plate XUX: 111, 112, 115, 129) Plate XVIN)eto apmoderare 
sized one, (Sphegina, Didea, Figs. 51, d, Plate XIII; 75, d, 76, Plate 
XIV; 100, d, Plate XIX) to a comparatively large mouth (Baccha, 
Chilosia, Rhingia, Figs. 21, 25, 26, Plate XI; 3, 4, Plate XV;.5; 11, 
Plate X- 32) 33, 34; 30, Plate XII; 102, Plate XVID), Ins position i 
varies from being sessile on the face of the globular or hood-like chitinous 
box (vide infra) as in Hammerschmidtia, Eumerus strigatus, Copestylum 
marginatum, Cynorhina analis, Milesia virginiensis, Helophilus, (Figs. 
115, 117, Plate XVIII) to being elevated at the apex of a tube, short 
and delicate in Helophilus spp., (Fig. 86, Plate XVI), Criorhina nigripes 
(Fig. 111, Plate XVIII) and Mesogramma (Fig. 45, Plate XIII, in 
some species of which it turns a complete loop before its termination), 
heavy in Rhingia, Chrysogaster spp., Pipiza, Sphegina, (Figs. 40, 41, 
Plate X; 19, 24, 26, Plate XI; 32, 34, Plate XII; 69, Plate XIV), longer 
and delicate in Criorhina nigra, still longer and heavy in other species 
of Criorhina, and long, very heavy and distorted in Baccha sp. In 
other cases it is continued to the termination of a long, sometimes 
extremely long and slender tube, single in Chrysogaster spp., Mallota 
posticata, Mixogaster breviventris, Crioprora cyanella (Figs. 118, Plate 
XVIII; 133, Plate XIX; 36, 37, 38, Plate X); double in Microdon and 
Ceriodes, (Figs. 129 to 182, Plate XIX); in the former the two tubes 
both on the median line, the split transverse, and one tube may be much 
shorter; in the latter the two placed right and left, the split longitudinal. 
And from being thus subtended by a rigid, chitinous support, we find 
variations to-a support, chitinous, basad, but delicate, inflated and 
collapsable at apex, (Chilosia, Syrphus, Chrysotoxum, Eupeodes Figs. 
7, 29; Plate XII: 49, 50; 53,59, Plate XIII. 134, Plate XIX), and toa 
condition in which it is surrounded by a delicate flexible and inflated 
hyaline membrane as in Sphaerophoria (Figs. 1, 60, 63, 64, 67, 68, 
Plate XV). 
