Article beginning on page 399.
Psyche 9:399-400, 1900.

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Psyche, Vol, 9.
Plate 5.
INVERTED HY POPYGIUM OF DASY LLIS AND LAPHRlA.



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PSYCHE.
THE INVERTED HYPOPYGIUM OF DASYLZIS AND LAPHRIA. BY ROBERT E. SNODGRASS, PULLMAN, WASH.
The Asilid genera BasyZZis and
Lathria present the curious anomoly of
having the hypopygium, i. e., the ninth
segment of the male, inverted.
Figures
I and so clearly show this condition in
D. grossa and B.flavicollis.
The writer is indebted to Professor
J. M. AIdrich, of the University of Idaho, for named material on which the fol-
lowing descriptions are based.
The hypopygium consists of a large
ovate structure carried by its larger end on a comparatively narrow neck formed
of the seventh and eighth abdominal
segments and their intervening mem-
branes (Fig. 10). 'Within the hypopy-
gium is a large cavity, the genital cham- ber, opening posteriorly. It has a thick swollen floor on which is carried the in- tromittent organ, and thin dorsal and
lateral walls. The dorsal wall presents
a large median notch reaching forward
almost to the base of the hypopygium.
The lateral walls are similarly, but less deeply, notched.
The lower part of the hypopygium is
theninth tergum (IX t.). It consists of
a large convex plate, oval to elongate-
ovate in ventral view, with the smaller
posterior end truncate. The posterior
end may be also deeply notched as in
D. grossa (Fig. 4) or it may be but
slightly concave as in D. flavicollis and L. vultur.
The upper and lateral parts of the
hypopygium consist of the ninth sternum
(IX s.). On account of the dorsal and
lateral notches of the hypopygiuni, the
sternum has the form of a hasal semi-
circular plate with two large dorso-lateral lobes projecting backward (Figs. I, 2, 4 and so, IX s.) Each of these lobes
carries, within the genital chamber, two pairs of large movably attached ap-
pendages (a and b). One pair (a) is
lateral and is articulated to the dorsal edge of the lateral notch oi the hypopy- gium (Figs. I, 5 and 10, a). Each of
these (Fig. 9) is laterally flattened and strongly curved dorsally, where it ends
in one or two heavy claws that project
out of the dorsal notch. The other pair
(b) is dorsal and is born by two lobes at the anterior angles of the dorsal notch of the hypopygi~~m (Figs. 2 and 5,b). These appendages (Fig. 8) vary considerably
in shape. They are generally bent some-
what laterally. In some species they
are expanded basally, in others termin-
ally ; in some they are prong-like, in




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400 ~ C ~ . [October, 1002
others they are spoon-shaped.
In L.
uzdtiir the tip of each is formed of three plates set at right angles to one another. The penis (Figs. 6, 7 and 11, fen.) is
a chitinous tube terminating in three
slender prongs. Apparently the seminal
passage divides into three tubes at the
bases of these and opens by three ap-
ertures at their tips. The penis (Fig. 6) is carried on an elevated support (Fig. 7) on the floor of the genital chamber. The three terminal prongs project posteriorly from the latter over the tenth segment.
Attached to the interior of the support
is a large muscle apodemc (Fig. I 1, a$.). On account of the inverted position of
the nintli scgment, the tenth segment
(X) comes to lie below the mouth 01 the
genital chamber instead of, as normally, above it. It is composed of the ordinary characteristic parts. There is a divided suranal plate (-fa) lying here below
the anus, and two elongated podical
plates ($04 lying above the anus.
The eighth segment is partially rudi-
mentary. It consists of a narrow curved
bar 1'orming the dorsal and lateral parts (Figs. 3 and I 0, VIII s) , and of a small plate (Figs. I, 3, 4 and 10, VIII f) ap- plied to the right lower aspect of the
base of the hypopygium. The eighth
segment is symmetrical in shape but
asymmetrical in position. Normally it
is almost hidden within the seventh
segment (Fig. I).
The rectum lies in the right side of
the body cavity of the hypopygium, turn- ing in mesially at the base of the tenth or anal segment. Hence, the hypopyg
ium must have revolved to the right
from above. If this is so, then the
small dextro-ventral plate of the eighth segment is probably the eighth tergum
which has revolved through only about
i5o0. The seventh segment is normal,
the revolution having taken place en-
tirely back 01 it. It is small and is
mostly concealed within the sixth
segment.
Explanation of Plate .
Fig. I, Dasj~llis grossa, lateral view of hypopygium ; Fig. 2, D. grossa, dorsal
view of hypopygium; Fig. 3, D. grossa,
eighth segment ; Fig. 4, D. grossa, ven- tral view of hypopygium ; Fig. 5, D.
$osticata, interior view of right half of ninth sternum, showing attachments of
appendages aand b ; Fig. 6, D. postit&,
dorsal view of penis ; Fig. 7, D. grossa, lateral view of ninth tergum and penis,
and tenth segment; Fig. 8, D. grossa,
appendages b ; Fig. 9, I). pssa, ap-
pendage a ; Fig. 10, D. ftavitollts, lateral view of hypopygium; Fig. I I D.ffavi-
tollis, lateral view of penis and its sup- port. VI i, VII /, VIII /, IX t, sixth to ninth abdominal terga; VI s, VII s,
VIII s, IX s, sixth to nintli abdominal
sterna ; X tenth segment ; a, lateral
appendage of ninth sternum ; b, dorsal
appendages of ninth sternum ; $57~)
penis ; 4, apodeme ; so, suranal plate ; fod, podical plates.




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