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PSYCHE.

THE INVERTED HYPOPYGIUM OF DASYZLIS AND LAPH)?IA.

BY ROBERT E. SNODGRASS, PULLMAN, WASH.

The Asilid genera 1)gsyllis and

Lathria present the curious anomoly ofhaving the hypopygium, i. e., the ninthsegment of the male, inverted. Figuresand o clearly show this condition in

.D. grossa and .D. flavicollis.The writer is indebted to Professor. M. Aldrich, 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 endon a comparatively narrow neck formedof the seventh and eighth abdominalsegments and their intervening mem-branes (Fig. o). Within the hypopy-glum is a large cavity, the genital cham-ber, opening posteriorly. It has a thickswollen floor on which is carried the in-tromittent organ, and thin dorsal andlateral walls. The dorsal wall presentsa large median notch reaching forwardalmost to the base of the hypopygium.The lateral walls are similarly, but tessdeeply, notched.The lower part of the hypopygium is

theninth tergum (IX t.). It consists ofa large convex plate, oval to elongate-ovate in ventral view, with the smallerposterior end truncate. The posterior

end may be also deeply notched as inD. grossa (Fig. 4) or it may be butslightly concave as in D. flavicollis andL. vultur.The upper and lateral parts of the

hypopygium consist of the ninth sternum

(IX s.). On account of the dorsal andlateral notches of the hypopygium, thesternum has the form of a basal semi-circular plate with two large dorso-laterallobes projecting backward (Figs. I, 2, 4and o, IX s.) Each of these lobescarries, within the genital chamber, two

pairs of large movably attached ap-pendages (a and b). One pair (a) islateral and is articulated to the dorsaledge of the lateral notch of the hypopy-gium (Figs. x, 5 and IO, a). Each ofthese (Fig. 9) is laterally flattened andstrongly curved dorsally, where it endsin one or two heavy claws that projectout of the dorsal notch. The other pair(b) is dorsal and is born by two lobes atthe anterior angles of the dorsal notch ofthe hypopygium (Figs. 2 and 5, b). Theseappendages (Fig. 8) vary considerablyin shape. They are generally bent some-what laterally. In some species theyare expanded, basally, in others termin-ally;in some they are prong-like, in

Psyche, Vol. 9. Plate 5.

INVERTED HYPOPYGIUM OF DASYLLIS AND LAPHRIA..

400 .PS CI-IE. [October, t9o2

others they are spoon-shaped. In Z.vultur the tip of each is formed of threeplates set at right angles to one another.The penis (Figs. 6, 7 and i, pen.) is

a chitinous tube terminating in threeslender prongs. Apparently the seminalpassage divides into three tubes at thebases 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. Thethree terminal prongs project posteriorlyfrom the latter over the tenth segment.Attached to the interior of the supportis a large muscle apodeme (Fig. , ap.).On account of the inverted position of

the ninth segment, the tenth segment(X) comes to lie below the mouth of thegenital chamber instead of, as normally,above it. It is composed of the ordinarycharacteristic parts. Thereis a dividedsuranal plate (sa) lying here belowthe anus, and two elongated podicalplates (pod) lying above the anus.The eighth segment is partially rudi-

mentary. It consists of a narrow curvedbar forming the dorsal and lateral parts(Figs. 3 and o, VIII s), and of a smallplate (Figs. t, 3, 4 and IO, VIII t) ap-plied to the right lower aspect of thebase of the hypopygium. The eighthsegment is symmetrical in shape butasymmetrical in position. Normally itis almost hidden within the seventhsegment (Fig. ).The rectum lies in the right side of

ing in mesially at the base of the tenthor anal segment. Hence, the hypopyg-ium must have revolved to the rightfrom above. If this is so, then thesmall dextro-ventral plate of the eighthsegment is probably the eighth tergumwhich has revolved through only about

5. The seventh segment is normal,the revolution having taken place en-

tirely back of it. It is small and ismostly concealed within the sixthsegment.

x2lanation of lYate

Fig. , l)asyllis grossa, lateral view ofhypopygium Fig. z, Z). grossa, dorsalview of hypopygium; Fig. 3, l). grossa,eighth segment; Fig. 4,/9. grossa, ven-tral view of hypopygium; Fig. 5, l).

osticata, interior view of right half ofninth sternum, showing attachments ofappendages a and b Fig. 6, /9. osticala,dorsal view of penis; Fig. 7,/9. grossa,lateral view of ninth tergum and penis,and tenth segment; Fig. 8, .D. grossa,appendages b; Fig. 9, Z). grossa, ap-pendage a; Fig. o, Z). flavicollis, lateralview of hypopygium; Fig. x, 1).jqavi-collis, lateral view of penis and its support. VI t, VII t, VIII t, IX t, sixth toninth abdominal terga; VI s, VII s,VIII s, IX s, sixth to ninth abdominalsterna; X tenth segment; a, lateralappendage of ninth sternum;b, dorsalappendages of ninth sternum )en,penis a_P, apodeme sa, suranal plate;

the body cavity of the hypopygium, turn- tod, podical plates.

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