242 BLOOD-SUCKING MUSCID^ [CH. 



that the proboscis forms a very efficient apparatus for piercing 

 the skin. Occasionally the proboscis is only partly chitinous 

 and is retractile, and the labella are large and fleshy, but even in 

 these cases strong teeth, capable of cutting through the skin, 

 are present. In other respects the proboscis resembles that 

 present in the non-biting Muscidae, being longitudinally grooved 

 on its dorsal surface, so as to ensheathe the epipharynx and 

 hypopharynx, which together form a tube, by apposition and 

 basal interlocking. The blood-sucking habit is equally well 

 developed in both males and females. 



Although Glossina and Stomoxys are the only two genera 

 that have been proved to carry infection, there is every possi- 

 bility that other members of the group may suddenly acquire 

 unenviable notoriety from this point of view, and therefore 

 we include the following table of the genera, taken from Alcock : 



Genera of Blood-sucking Muscidce. 



f Arista feathered only on the dorsal surface, individual hairs being also 

 feathered. Proboscis with a bulbous base and very slender shaft. 

 Maxillary palps long and slender, forming a sheath round the pro- 

 boscis. Fourth longitudinal vein curved in its proximal portion so 

 as to enlarge the anterior basal cell distally and to contract the 

 discal cell basally ; and sharply bent forward in its distal portion 

 in line with the posterior cross-vein so as to nearly close the first 

 posterior cell at a point much anterior to the tip of the wing. 

 Abdomen composed of seven visible segments . . . . =Glossina. 

 Individual hairs of arista not feathered. Shaft of proboscis not remark- 

 ably slender. Maxillary palps not forming an obvious sheath for 

 the proboscis. Fourth longitudinal vein not markedly sinuous in 

 its proximal portion and bending forwards in its distal portion at 

 a point considerably beyond the posterior cross- vein. Abdomen 

 composed of four visible segments . . . . . . = 2 



{Maxillary palps slender, less than half the length of the proboscis. 

 (Arista feathered dorsally only. Third longitudinal vein with some 

 bristles on its proximal part.) .. .. .. .. = Stomoxys. 

 Maxillary palps more or less spatulate, almost as long as the proboscis, 

 always much more than half its length . . . . . . =3 



C Proboscis chitinous in all its extent, the labella small . . . . =4 



Proboscis with the distal part, and large labella, fleshy. Terminal 

 fleshy part of proboscis reflexed beneath the chitinous part in repose. 

 Arista feathered dorsally and ventrally ; third longitudinal vein not 

 bristly ; fourth longitudinal vein abruptly bent so as nearly to 

 close the first posterior cell 



=Phil(zmatomyia (including ? Pristorhynchomyia). 



