3i6 ME. WALTER WESCHE ON THE GENITALIA OF 



represent an aborted organ, as in Oliviera lateralis; but it often develops hooks, or 

 processes like the paraphalli, without any articulation or break in the structure. 



Bibionld(B. — In Bibio horliilanus and B. marci it is a ribbon-like process supporting 

 the appendages and surrounding the curious plate which forms the penis, and which 

 itself is a part of the theca (PI. 23. fig. 4). In Scatopse notata it supports the membrane 

 of the penis (PL 23. fig. 7). 



Culicklce. — In Culex pipiens, Linn., and an undetermined species, it is a membrane 

 supported by lateral chitinous processes, an arrangement similar to that found in 

 certain Tipulidae (PI. 23. figs. 13, 15; Pi. 24. fig. 29). 



Tipulidce. — In Tipula oleracea it is a very clearly differentiated part, supporting a pair 

 of appendages and fused at the base with the double apodeme. The penis works freely 

 through it, and there is also a central rod, which I regard as a part of the theca, which 

 forms a third apodeme. These organs have muscular attachments which practically 

 anchor the theca, as that part is not extruded, the long flagellum being pushed through 

 it (PL 24. fig. 23). 



In Bachfyrrhina maculosa, Meig., ai'e two chitinous pieces that represent the atrophying 

 apodemes and support tlie theca, which is well developed and carries the appendages, 

 but has not the central process of Tipula oleracea (PL 24. fig. 29). In Gynoplislia bella, 

 AVestw., an Australian insect, as w ell as in an undetermined British Tipulid, this part is 

 very extraordinary, developing numerous hooks and supported by lateral columns as in 

 the Culicida? (PL 23. fig. 15). 



In Btychoptera scutellaris, Meig., the levers appear absent, but the theca is much 

 developed. I have not succeeded in finding the orifice of the ejaculatory duct, but 

 I have had but little material for examination (PL 24. fig. 20). 



St7'atiomyiidce. — In Berls vallata it is attached to the last segment of the abdomen ; 

 it does not enclose, and is not soldered to, the penis, but appears to act as a grooved 

 cliannel to guide it (PL 24. fig. 33). 



Tabanidce. — In Tabanus bromius the theca is quite similar to that of Bachyrrhina 

 maculosa, but is articulated to the double apodemes, which are well-developed (PL 29. 

 fig. 109). In Bangonia longlrostris the part has much the same form. 



Asllidce. — In the Asilidse is strongly chitinized, and broadening out at its bases 

 contains the ejaculatory sac (PL 24. fig. 38). 



Empidce. — InBJmjns stercorea the theca has developed paired barbs, which are probably 

 homologous with the paraphallus and the hypophallus (PL 25. fig. 39). In Silara cilijjes 

 a number of barbed serrations cover a very pronounced organ ; the penis is held in 

 a neat appliance, through which it is extruded or retracted (PL 25. fig. 41). 



Bolichopodidce. — In Boliclwpus plumipes, Scop., and other species of this genus, the 

 whole segment is fused witli the theca, tliough a suture can l)e detected (PL 25. fig. 43). 

 In B. festivus, Haliday, paired barbs are found ; in B. griseipennis only a single 

 pair appears (PL 25. figs. 44, 50). 



SyrphidcB. — In Catahomba pyrastri an arrangement is found not unlike that in 

 Bibio hortulanus; the theca surrounds the penis witli an enclosing -nail, which supports 

 the appendages (PL 25. fig. 53). In EristaUs tenax and Syritta 2)ipcHS this part is 



