344 ME. WALTEE WESCHE ON THE GENITALIA OF 



XJs(,_ — From the situation of the part, the number of spines and hooks usually 

 found on the organ, it is obviously used in holding the female. 



Homologies with ovipositor. — It appears to homologize with the ventral portion of the 

 fourth segment of the abdomen of the female, counting the last segment of the ovipositor, 

 that bearing the valves or egg-guides, as the first. Properly speaking, the first segment 

 of the abdomen is that next the thorax, but, as the number of the segments is variable, 

 the only vray of comparing the genitalia of the sexes with exactness is to count that 

 bearing the valves as the first segment. 



{d) The Exteemity op the Penis. 



Structure. — This part has to be diff'erentiated from the tlieca or cover, therefore for 

 the present pui'pose I shall regard it as the orifice of the ejaculatory duct. It is 

 mostly a delicate fiexible hyaline membrane with characteristic triangular, more or less 

 cliitinous plates often forming part of the structure, or it may be a free, transparent 

 chitinous tube as in the Tipulidse. 



3Iycetoj)hilidce. — In Sciara tJiomce (Linn.) it is diff3cult to make out, but appears to 

 l)e a structureless liyaline stile (PI. 23. fig. 1). 



Bihionidce. — In Bibio hortulanus (Linn.) and B. marci (Linn.) it appears as a plate, 

 with the edges bent over, which do not meet but are covered by a delicate membrane. 

 It has the appearance of the organ as seen in some Coleoptera {JUermestes). In Scatopse 

 notata it is membranous, and with the character of the whole organ approximating 

 to that in the Muscidse in the external, and to that of the Tipulidse in the internal 

 organs (PL 23. fig. 7). 



Ciilicidce and Tipulidce. — I have failed in trying to dissect out this part in the Culicidie 

 as well as in the Tipulid Oynoplistia bella, but a comparison of these parts Avith 

 those of Tiptda oleracea and Bachyrrliina maculata, Meig., easily supplies the lacunae. 

 In these insects a long tube or flagellum proceeds, bending in a circle in the process, 

 from the ejaculatory snc, of which it forms a part and continuation, to an organ which is 

 evidently the tbeca, passing longitudinally through a passage in it, and working quite 

 freely in the passage; it is capable of extrusion and retraction. It is contained in 

 a membranous envelope, noticed by Dufour, which has been thought to be the containing 

 membrane of the spermatozoa, but, as I shall show later, tliis does not agree witb my 

 explanation of the working of the apparatus (PL 23. fig. 15 ; PI. 24. figs. 23, 24, 29). 



Bhyphidce. — In Bliyplius fenestralis this part in the interior presents the appearance 

 of a long tangled thread, and it is similar in E. p>uncfatus. 



StratiomyiidcB. — In Be7'is vallata (Forster) it is a hyaline tube, less stiliform in shape ; 

 springing from the same base, it has on either side two knife-like blades with serrated 

 edges at the extremities (PL 24. figs. 32, 33). 



Tabanidce. — In Tabanus bromius two slender stiles seem capable of extrusion througli 

 the theca ; they are enveloped in a delicate membrane, much covered with fine blunt 

 setge (PL 29. fig. 109). 



Asilidce. — In the Asilidae an arrangement is found which is somewhat similar to that 



