354 ME. AVALTEE. WESCHE ON THE GENITALIA OF 



Lonchceidce. — In Toxoneura nndiebris it cau be traced in a similar forked form at the 

 base of the j^cnis (PL 30. tig. 122), and in a fused form in L. nigrlmana. 



Se2)sid(e. — In the Sepsidse the part is very clearly seen to be a paired organ, though it 

 becomes fused at its lower end (PL 28. fig. 99 ; PL 29. fig. 101). 



jjsg — These organs in all their conditions are attached to powerful muscles, which 

 rotate the penis from its position of rest as in the Blow-fly, or extrude it as in Tabanus 

 or Bihio. 



Homologij loith ovipositor. — In the base of the ovipositor of Musca domestica are two 

 rods which fuse at their lower end for no apparent reason ; it has occurred to me that 

 they represent these apoderaes. Firstly, because they are at the base of all the other 

 rods save one, as the apodemes are normally at the base of the theca ; and secondly, 

 because they are paired organs, agreeing in this respect with the apodemes in two 

 important particulars (PL 29. fig. 107). 



{n) Ductus ejaculatorius. 



Structure. — This part is usually a delicate hyaline membrane. In Si/ritta pipiens it 

 difi'ers, having the appearance of a striated muscular tube with double walls, which 

 spread out to form the ejaculatory sac, tliis peculiar structure ending here. 



Homology with ovipositor. — It is obviously homologous with the vagina of the female 

 insect. 



(o) " Sacculus ejaculatorius." 



structure. — This most important organ of the genitalia undergoes bewildering 

 changes of shape and situation ; it is usually a hyaline pouch with the apodeme 

 adhering to it, proceeding downwards from the penis ; or it may be a chitinous sac, as 

 in the Tipulidre, or a part of the theca, as in the Asilidae and Dolichopodidfe. 



It will be convenient to describe the apodeme with the sac, so before proceeding to 

 more details I shall give tlie structure of the 



(p) Ejaculatory Apodeme, 



Structure. — This is a minute rod in many species, not unlike the microscopic lever 

 that is found attached to eacli spiracle, but is more often spread out at the base into a 

 spatulate or fan shape, to afford a larger space for the attachment of muscles. This 

 part, when so modified, has the curious laminated structure noted in the double 

 apodeme. 



In wliat may be termed the head, that is to say the part in contact with membrane, 

 or which is used to close the sac, a number of lighter circles, not unlike bristle-sockets, 

 may be seen in some species. They are characteristic, but they require high powers and 

 skilful manipulation to reveal. I have seen them in Asilus crabronifonnis, Linn., the 

 Asilid figured, and in the very distantly related Glossina palpalis and G. pallidipes. 



Nomenclature. — Lowne noticed the part, in Calliphora, calling it a sclerite * ; but this 



* ' Blow-fly,' p. 665. 



