MUSCINM 



905 



feed. Such infective matter appears to be attached to their heads 

 (mandibles), legs, wings, and bodies. Klein has grown the 

 typhoid bacilli from flies caught in an infected area. 



Flies have long been accused of being the spreaders of dysentery, 

 and recently this view has been experimentally proved by several 

 authors, including one of us. Other diseases, including intestinal 

 myiasis, are said to be spread by flies. 



The flies found by Newstead in houses in Liverpool, or bred from 

 refuse and excreta, were Musca domestica in quite 90 per cent, of 

 all flies, while the other species met with were — Calliphora erythro- 

 cephala, the blow-fly; Scatophaga stercoraria, the dung-fly; Bor- 

 borus equinus, a small fly; Stomoxys calcitrans, the stable-fly; Fannia 

 canicular is ; F. scalaris ; Anthomyia radicum, the root -fly; Psy- 

 choda phalcenoides , the owl-midge. 



Morphology. — The vertex shows three oceUi, situated on a slightly raised 

 ocellar triangle, which is surrounded by another triangle, the vertical triangle. 



Between the upper and lateral edges of the clypeus (face) and the lower edge 

 of the epicranium can be seen the crescentic opening of the ptilinum. - 



Fig. 471. — -Anatomy of Musca domestica. 



(After C. J. Martin.) 



Labella; P., proboscis; 5.D., near salivary duct; g., gullet; S, mid-gut; 

 i., intestine; C, sucking stomach; T, rectum. 



The proboscis consists of the rostrum, the haustellum (proboscis proper), 

 and the labellae. The rostrum is a truncated cone containing the pharynx; 

 the haustellum is grooved anteriorly to contain the labrum, epipharynx, and 

 the hypopharynx. Posteriorly it is strengthened by a sclerite called the 

 ' theca, ' which distally carries the fork (furca) . 



The labrum and the epipharynx, with the hypopharynx, as is usual, form 

 the pharyngeal tube, while the hypopharynx contains the salivary or hypo- 

 pharyngeal tube. The labellae are complicated organs with a number of 

 channels (pseudo-tracheae) on their distal surface. 



Each labella has lobes anterior, middle, and posterior, with respectively 

 twelve, twenty-one, and three channels, which eventually run to the oral 

 aperture, which lies at the base of the oral pit. This pit is kept open by two 

 discal sclerites. In the oral pit the pseudo-tracheae cease, and the sides of the 

 channels are covered by overlapping teeth. 



The pro- and meta-thoraces are much reduced, while the mesothorax is well 

 developed, and shows a typical structure. The venation of the wings may be 

 briefly described by saying that the costa and subcosta are well marked, and 

 the usual costal and first costal cells are present. Radius i cuts off the sub- 

 costal cell; R. 2 and 3 the first radial, and R. 4 and 6 the third radial; while 



