240 CYCLORRHAPHA SCHIZOPHORA [CH. 



(i) Acalyptratae. 



The squamae are always small, or vestigial, so that they do 

 not conceal the halteres when viewed from above. The 

 auxiliary vein is often indistinct or vestigial, or close to the first 

 longitudinal, with which it may be fused. The basal cells are 

 smallj and the posterior ones indistinct or wanting. The males 

 are never holoptic and the front is never markedly constricted. 

 The thorax is without a complete transverse suture and the 

 posterior callosity is usually absent. The members of this 

 group are never large flies, but usually small, or very small. 

 None of them are known to suck blood, but certain species, 

 e.g. Sepsis, are probably concerned in the transmission of 

 disease^. 



(2) Calyptratae. 



The squamae are well-developed, never vestigial, and 

 generally conceal the halteres when viewed from above. The 

 auxiliary vein is always distinct along its whole course and the 

 first longitudinal is usually of considerable length, never very 

 short. The males are often holoptic or the front markedly 

 constricted. The thorax has a complete transverse suture in 

 front of the wings and a posterior callosity is present. The 

 members of this group are generally flies of moderate or con- 

 siderable size and are never very small. The house-fly and 

 tsetse-fly are two well-known examples of this large and im- 

 portant group, which is of the highest economic importance. 

 Williston divides them into six families, of which the only one 

 that we shall consider is the Muscidse. 



Synopsis of Families of Calyptratce. 



f Mouth and mouth-parts small or vestigial; first posterior cell closed 



' •{ or nsLTTOwed [except in Gastrophilus). Bot-flies .. =OestridcB 



L Mouth of usual size, mouth-parts not vestigial . . . . . . =2 



C Hypopleurae with a tuft of bristles ; first posterior cell narrowed or 

 I closed . . . . . . . . . . . . , . . . = 3 



I Hypopleurae without a tuft of bristles ; first posterior cell narrowed or 

 L fully open in the margin . . . . . . . . . . = 6 



^ Vide Graham-Smith, G. S. (1913), Flies and Disease. Non-hloodsucking 

 Flies (Cambridge University Press). 



