INTRODUCTION 



ROBBER FLIES OF THE WORLD 



13 



Explanation, 



Text-Figures 4 and 5 



1, Eighth tergite. 



2, Eighth sternite. 



3, Epandrium. 



4, Hypandrium. 



5, Gonopod. 



6, Superior forceps. 



7, Aedeagus. 



8, Penis guides (or sheath). 



9, Proctiger. 



10, Clasper. 



11, Pseudoclasper. 



12, Paralobus. 



13, Hamate process. 



14, Cavity of superior forceps. 



15, Cut edge of superior forceps. 



16, Cut edge of gonopod. 



17, Aedeagus sheath. 



18, Cavity of gonopod. 



19, Penis sheath. 



II 10 5 4 



Text-Figure 5. — a-c, e, Diogmites platypterus Loew: a, exterior 

 view of gonopod with processes; B, medial view of gonopod with 

 processes; c, aedeagus and sheath from ventral aspect; e, 

 lateral aspect with true right gonopod and whole proctiger 

 removed. D, Astochia sp., the superior forceps removed. 



rior forceps do not begin until some distance from the 

 base of the segment. 



Between the superior forceps (epandrium) and the 

 ninth sternite, there is usually a well developed, paired, 

 lateral organ somewhat shorter than the epandrium 

 and attached to or borne by the ninth sternite. This 

 is the inferior forceps of Oldroyd (1938), and to avoid 

 the additional use of the word forceps, I have uni- 

 formly called this structure the gonopod, since it is 

 borne dorsally from the hypandrium. This lateral 

 structure appears to be equivalent to the gonopods of 

 authors. Beyond this point the confusion with regard 

 to the characteristic, distal processes so often seen in 

 the Asilidae grows greater, and since clear evidence of 

 segmental character is wanting, I have rejected the use 

 of the terms styli or surstyli for these processes. It 

 will be noted that the lateral gonopod often bears a 

 medial, more or less upright, arched and sublamellate 

 process tending to enclose the aedeagus (distiphallus) : 

 I have followed Oldroyd (1938) and others in calling 



this lateral and medial appendage the clasper, when it 

 is clearly borne by the gonopod. This structure, the 

 gonopod, when present tends to enclose the penis 

 guides when these are present, which in turn encloses 

 the aedeagus. However, the clasper is sometimes 

 either lacking or greatly reduced. Again, the clasper 

 may be double, with four structures in two pairs (two 

 on each side) of nearly equal prominence and each 

 arising, as in Astochia Becker, from the medial base of 

 the gonopod. The outermost of these structures are 

 here called pseudoclaspers. There may be a similar 

 structure arising rarely from the inner wall of the supe- 

 rior forceps as in Oligoschema Becker, sensu stricto, 

 and I call this the paralobus. The accompanying text- 

 figures 4 and 5 show graduated dissections in lateral 

 aspect of a representative of each subfamily. 



Attention should be called to the rotation or inver- 

 sion of the male terminalia. A considerable literature 

 has arisen on the controversial subject of the mechanics 

 and mode of inversion. Those interested in the sub- 

 ject are referred to Lamb (1922a). Botation usually 

 takes place during copulation in the Dasypogoninae, 

 but the terminalia are permanently rotate 180 degrees 

 in the subfamily Laphriinae. In Asilinae and Lepto- 

 gastrinae they are not rotate at all and the superior 

 forceps and accompanying proctiger are always dorsal 

 in position. Since in Dasypogoninae the rotation oc- 



