1974] 
Cooper — Boreus 
95 
Diptera (as Empis) , and Coleoptera ( Lomechusa ) (Meisenheimer 
1921, Richards 1927), as well as for aradids (Heteroptera) (Usinger 
and Matsuda 1959). For the majority there is little information on 
the correlation involved, but it is probably generally inverse, with 
the anus of the female unobstructed, as in Boreus . The similarities 
cease here, however, for so far as I am aware the species of Boreus 
are unique in their adaptation to, and practice of, a reciprocal intro- 
mission — namely a concurrent passage of the female’s gonapophyses 
into a specialized genital pocket within the male, and of the aedeagus 
into the common oviduct (fig. iC). This curious arrangement was 
first commented upon by Cockle (1908, 1914), and later by Steiner 
( I 937) an d Cooper (1940), but it has not properly been described. 
Projecting cephalad from the medio-dorsal aspect of the gono- 
coxites of the male, there are two sclerotized laterally flattened straps, 
the dorsal apophyses of the gonocoxite, that expand medially and 
unite to forjn a thin, broad, pigmented roofing plate that lies below 
the anus (figs. 2A, B ; fig. 4, Cooper 1972). The more dorsal anus 
is itself enclosed by sclerotized dorsal and ventral proctigeral plates 
(segments X + XI?) (fig. 2A; fig. 3, Cooper 1972). 8 Ventral to 
the gonocoxital roofing plate, or dorsal portion of the gonobase, there 
is a broad, sclerotized band overlying the dorsum of the aedeagus 
(figs. iC, 2A, B; also fig. 4 Cooper 1972). A wide, enclosed, shal- 
low but elongated pocket is thus formed between the dorsal gonobase, 
the muscles of the gonocoxites, and the sclerotized band over the 
aedeagus. In the unmated male at rest, this pocket (which I call the 
endandrium ) curves downward under the epandrium (fig. 2B). 
Just prior to insertion of the aedeagus, the gonapophyses (sternites- 
VIII, or “ventral valves of the ovipositor”) are thrust by the male 
into the endandrium. The main fields of caudally-directed spines on 
the bosses to each side of the epandrial notch (fig. 2A) catch on the 
outwardly directed denticles of the blades of the gonapophyses, pre- 
venting slippage outwards as the gonapophyses are initially forced, 
ratchet-like, more and more deeply into the endandrium. Once fully 
inserted within the endandrium, the gonapophyses are locked in place 
there by the gonostyles of the male. Not only is the blade of each 
gonapophysis grasped tightly between the apex and inner tooth of a 
gonostyle, but that inner tooth of each gonostyle is in turn engaged 
by being seated into the lateral basal notch of its corresponding gona- 
pophysis (fig. iB cf. A, C, arrow). That union so forcibly locks the 
8 The proctigeral plates (= segment-XI) in the female of Boreus notoper- 
ates are similar to those of B. brevicaudus, described by Byers (1961). 
