BOTH THE SEXES IN DIPTEEA. 347 



much enlarged and has developed levers at the base, by means of which it can be rotated 

 (PL 25. figs. 56, 67, 58). 



Muscidce.- — In many of the Muscidte the theca not only forms a guard to the tvibe, 

 but is also a platform which is fused with and supports the part called by Lowne the 

 bulb * (the lower part of the chitinous process which sustains the ejaculatory orifice), 

 the appendages (the spine, palpi, and hooks), as well as the paraphallus and hypophallus 

 (PI. 26. figs. 62, 68). In Glossina the theca forms a wall round the double apodeme 

 (PL 27. figs. 78, 84). 



LouchceidcB. — A rery beautiful adaptation of this part is found in Toxoneura muliehris, 

 Harris. This insect has a long ciliated penis with considerably more chitinous structure 

 than TJlidia nigripennis, Meig. This penis at its base passes through a plate which bears 

 the usual appendages, and is obviously the theca (PI. 30. fig. 122). The same structure can 

 be made out in Lonchcea nigrimana, Meig. In Palloptera tistulata, Pall., a remarkable 

 chitinous process is found at the extremity of the ciliated ribbon which forms the male 

 organ ; a series of folds enclose the tube ; from this rises a small column carrying the 

 ejaculatory dvict ; attached to the folds is a single relatively large plate formed into a 

 hook ; this appears to be the upper part of the theca, much separated from, its base, 

 which is, as in T. mullebris, a chitinous ring bearing some appendages. 



Uplvjdrklce. — In Farijdra coarctata two rings of chitin support the part carrying the 

 hyaline membrane of the duct; the larger ring bears two appendages (PL 29. fig. 111). 



Homology with ovipositor. — The homology of this part with any distinct part of the 

 ovipositor is not obvious, but possibly it may be represented in Mxsca domestica by the 

 rods on the first two segments, counting, as before, the segment bearing the egg-guides 

 as the first. 



(/) The Paraphalli. 



Structure. — There ai*e two lateral rods springing from the back part of the theca and 

 coming forward. They are always strongly chitinized, and characterized in the genus 

 Ifusca by minute transverse serrations on the extremities. 



Nomenclature. — They were first pointed out, and are named, by Lowne. 



Empidce and iJoUchopodidce. — They are only markedly present in the Muscidte ; and 

 we seem but to get a hint of their existence in the Empida; and Dolichopodidae, 

 where the barbs on the theca already alluded to are probably homologous (PL 25. 

 figs. 39 & 4i). 



Si/rphidcB. — In Syritta pipiens the theca is hollowed out at the point, and in this half 

 segment of a circle are one or two curious processes which may, or may not, represent 

 these parts (PL 26. fig. 56). 



In EristaUs tenax the theca is continued up to two serrated blades, which appear to 

 be the paraphalli (PL 26. fig. 58). 



Iluscidcc. — In Scu'copliaga these parts are represented by two plates springing 

 laterally from the theca above the bulb, quite unlike the appearance of the parts in 



* ' Blow-flj-,' p. 738. 

 SECOND SERIES. — ZOOLOGY, VOL. IX. 51 



