148 ENTOMOLOGY FOR MEDICAL OFFICERS 



and the squamje are small. These flies are often found on 

 excrement, and some of them are predaceous on flies and 

 other insects. 



(b) Calyptrate Muscoidea. 



The squamae are large and generally conceal the halteres 

 in a dorsal view ; the subcostal vein is distinct, and the ist 

 longitudinal vein is of good length ; the scutum is completely 

 bisected by a transverse suture in front of the wings ; 

 generally in the male the eyes are approximated. This 

 division includes an enormous number of species, many of 

 which are of importance to the sanitarian and pathologist ; 

 they are often grouped in six " families," which, however, are 

 not always quite clearly defined one from another and are 

 not universally recognised. The following table is taken 

 from Williston's North American Diptera: — 



Synopsis of Families <?/" Calyptrate Muscoids. 



/Mouth and mouth-parts small or vestigial (Estridce. 



I Mouth and mouth-parts well formed = 2. 



(Hypopleura with a tuft of bristles ; ist posterior cell narrowed or 

 closed = 3. 



Hypopleura with no tuft of bristles ; ist posterior cell narrowed or 

 fully open = 6. 



('Arista usually bare, sometimes pubescent ; body and legs very 



3- I bristly Tachinida. 

 '-Arista feathered or distinctly pubescent = 4. 

 rArista feathered, but not to the tip ; discal bristles rarely present 



4- \ on the anterior segments of the abdomen Sarcophagida. 

 '■Arista feathered or pubescent to the tip = 5- 

 rAbdomen usually with discal bristles on its anterior segments ; 



5- \ legs usually long Dexiida. 

 '■Abdomen with no discal bristles ; arista feathered Muscida. 



(First posterior cell narrowed or closed ; arista feathered 

 to tip Muscida. 



First posterior cell slightly or not at all narrowed ; arista feathered, 

 pubescent, or bare Anthomyida. 



Family MUSCID^ {sensu restrictd). 

 To the medical officer this is one of the most important 

 of all the families of insects, as it includes a considerable 

 number of dangerous pests of man, of which the house-fly 

 is the best known, and the tsetse-fly is, perhaps, the most 

 notorious and most formidable. 



