BOTH THE SEXES IN DIPTERA. 349 



Nomenclature. — Lowne calls it " the spine " ; I observed it in Scatophaga lutaria, 

 Fabr., ras an articulated organ, and thought it might be homologous with the " titillator " 

 in Periplaneta orientalis, the hook which Lowne suggests is used in the transference of 

 sjiermatophores * from the male to the female organisms. 



BoUchopodidce, — I cannot find any trace of this part in the families of Diptera till I 

 come to the Dolichopodidfe ; there it is large and well developed, and in company with 

 the other appendages to the theca (PI. 25. fig. 45). 



My identification of this part as the unpaired lancet under the hypopygium of 

 Dolicliojms is confirmed by the observations of Mr. Robert E. Snodgrass in his paper on 

 the genitalia of that family f . 



A number of species show the spinus in its usual position as shown in PI. 25. fig. 43, 

 though the part varies much in shape. But when the appendages are absent from this 

 situation, as in Psilopa sipho, the penis is surrounded by the theca, which supports two 

 leaf-like lateral processes, and between them a single median stile which I recognize as 

 the spinus. 



Muscidce. — It is absent in Sarcophaga carnaria and Oliviera lateralis (PL 26. fig. 60 ; 

 PI. 29. fig. 112), but it is generally present in the Muscidae (PI. 26. fig. 68 ; PI. 27. fig. 85). 



LonchceidcB. — One of the most curious m.igrations of this part is in the Lonchseidse. 

 In the Dolichopodidse we have found it near the base and at the extremity of the penis, 

 and also in Toxoneura muliehris, Harr., it appears to be at the base of the long ciliated 

 ribbon which forms that organ (PI. 30. fig. 122), while in Palloptera -mtulata. Fall., it 

 appears as a relatively large hook, symmetrical in shape and articulated to the rather 

 complicated chitinous part which forms the extremity of the penis, which in this 

 species also consists of a long ciliated ribbon. 



Use. — In use it fits into a fold of the ovipositor, as can be seen in Berlesi's remarkable 

 section of Musca domestica " in copula" +. 



Homologij. — It is obvious that its homology in the ovipositor must be looked for after 

 the determination of the homology of the theca. 



{i) FORCIPES INTERIOKES. 



structure. — These are two small blade-shaped hooks on both sides of the theca, 

 generally articulated ; they are more or less highly chitinized, with very short sharp 

 spines springing from sockets ; the surface is usually smooth. 



Nomenclature. — Lowne calls them " posterior gonapophysis," but this is obviously 

 indefinite, and I prefer my name of " forceps interior," as not only more definite, but 

 descriptive of the part. 



MycetophiUdce. — In Sciara thoma; they are probably the paired blades springing from 

 the root of the adminiculum (PI. 23. fig. 1). 



Bihionidce. — In Bihio hortulanus they are difficult to differentiate, but I think are 



• ' Blow-fly,' p. G64. 



t " Hypopygium of the DolichopodidsD," Sept. 28, 1904. Proc. Cal. Acad. Science, ser. 3, vol. iii. Zool. no. II. 



X Eiv. Patol. Vegetale, ix. (1902). 



51* 



