BOTH THE SEXES IN DIPTERA. 345 



of JBeris, but the stile, obvious in that genus, is quite absorbed by the chitinous theca 

 (PL 24. fig. 38). 



Empld(C. — Nearly the same form is found in the Empidaj, though here the tube is 

 again quite stiliform. Empls stercorea, Linn., is the simplest combination that I am 

 acquainted with ; the part is readily seen on the pinned insect as a long stile. On a 

 prepared specimen the junction with the theca is seen even with the lower powers of the 

 microscope (PI. 25. fig. 39). The part is practically the same in Hilara cilipes, Meig., 

 but with more elaborate surroundings (PI. 25. fig. 41). In the ovipositor of the female 

 is a curious notched process which may possibly act as a guide to the delicate fiagellum 

 (PL 25. fig. 42). 



BolichopocUdce. — In spite of the greater development of the holding organs, the 

 structure of the penis in the Dolichopodidae shows a close relationship to the Stratio- 

 myiidse, the Asilida?, and the Empida?. The hyaline stiliform tube has developed 

 processes, presumably of vise in coitus, serrations as in Dollchopus griseipennis, Stannius, 

 and a leaf-shaped excrescence in Z). nohilitatus (Linn.) (PL 25. figs. 43, 44, 49, 50). 



Syrphid(S. — In the Syrphidae the part is often a flexible membrane, as in Catabomha 

 pyrastri, Linn. (PL 25. fig. 53). In Eristalis tenax (Linn.) and Syritta pipiem (Linn.) 

 the ejaculatory duct opens into a horny box situated at or near the extremity of the 

 theca (PL 26. figs. 56, 57, 64). In Sphcerophoria scripta (Linn.) it consists of a 

 membrane studded with the usual triangular plates ; this is capable of inflation, and 

 when in that condition takes a tricuspid shape. 



Iluschhe. — In Sarcojihaga carnaria (Linn.) and the majority of the Muscidae, calyptrate 

 and acalyptrate, it is a hyaline flexible membrane. In Glossina tachinoides, WestM^, 

 this part has membranous Avings, studded with minute plates as in <S'. scripta, and 

 capable of inflation or erection, as I have demonstrated by alternately raising and 

 lowering the cover-glass. 



Acalyptra/ce. — In the Ortalidse, Trypetidae, and Lonchteidae it is a long membranous 

 tube, normally rolled on itself as a watch-spring is coiled, and when extruded not unlike 

 an ovipositor in appearance (PL 28. fig. 96). 



Ephydridce. — A very peculiar shape is found in NotiphUa niyricornis, Stenhammar, 

 where a membrane, studded with aculeations of vai-ious size, rises from a chitinous 

 theca (PL 28. fig. 98). The part in Parydra coarctata, EalL, is much like that in 

 Bibio hortulanus. This small fly has several peculiarities about the structure of the 

 mouth-parts that suggest tliat it is of very archaic type (PL 29. figs. 110, 111). 



Homology with ovipositor. — This part appears to be homologous with the membranous 

 structure of the ovipositor. This hypothesis is strengthened by the fact that in the 

 Ortalidae the penis has no chitinous parts except at the extremity. 



{e) The Tueca or Penis-sueath. 



Structure. — This is the chitinous case that protects the ejaculatory duct ; it is always 



highly chitinized, often with an anterior suture. It may be quite simple or consist of a 



number of plates. "When appendages are present it invariably supports them, whether 



articulated or not. No socketed hairs or bristles have been noticed, unless thev 



