FLIES FOUND IN HOUSES 



I I 



wing root " (Hewitt, 1907, p. 412). " Possibly these facilitate the 

 opening and closing of the wings " (Alcock, 19 11, p. 37). Behind 

 the wings the pair of Jialteres — commonly called balancers or 

 poisers^ — is placed, the most characteristic of all the dipterous 

 structures. They are believed to be the homologues of the hind 

 wings, though their exact functions are far from clear. " Each 

 consists of a conical base on which are a number of chordonotal 

 sense-organs, and on this base is mounted a slender rod, at the 

 end of which a small hemispherical knob is attached" (Hewitt, 

 1907, p. 413). They are provided with muscles at the base and 

 can, like the wings, execute most rapid vibrations. In the 

 MtiscidcB the squama covers the halter like a hood. Notice 

 should also be taken of the large bristles (if they exist) on the 

 thorax as they are of importance in the classification of some 

 groups. 



Each leg consists of five segments — coxa, trochanter, femur, 

 tibia and tarsus — the latter being composed of five segments. 

 The last tarsal segment carries a pair of clazvs, and below them 

 there is usually a pair of membranous pads or pulvilli; between 

 these there is often a small median appendix. " The pulvilli are 

 covered on their ventral surfaces with innumerable, closely set, 

 secreting hairs by means of which the fly is able to walk in any 

 position on highly polished surfaces" (Hewitt, 1907, p. 414). 



The abdomen, or hindmost division of the body, is composed 

 of several segments, and generally 

 shows lighter or darker markings, 

 useful in distinguishing one species 

 from another. "In the house-fly 

 the total number of segments which 

 compose the abdomen is eight in 

 the male, and nine in the female. 

 The visible portion consists appar- 

 ently of four segments." Actually 

 there are five segments but the first 

 is much reduced and fused with the 

 second. " The segments succeeding pig. 5. Abdomen of female house- 



the fifth are greatly reduced in the Ay showing the extended ovi- 

 ■^ positor. (After Hewitt, 1907, 



male, and in the female form the pi. xxill, fig. 8.) 



