26 THE EXTERNAL STRUCTURE OF MUSCA DOMESTICA 



Tlie Legs. 



The three pairs of legs are composed of the typical number of 

 segments. Each consists of coxa, trochanter, femur, tibia, and 

 tarsus. The coxae are the only segments that show any consider- 

 able difference in the three pairs of legs. The anterior coxae are 

 comparatively large and boat-shaped, the intermediate coxae are 

 smaller and their separate sclerites more marked ; the coxal plates 

 of the intermediate coxae are shown in fig. 6 (cp.). The coxal 

 joints of the posterior pair of legs are almost similar to those of 

 the intermediate pair. The anterior femora are shorter and stouter 

 in the middle than those of the intermediate posterior pairs of 

 legs. The anterior tibiae are also shorter than those of the succeed- 

 ing legs. The anterior tibiae are covered on their inner sides with 

 closely-set, orange coloured setae which serve as a comb by means 

 of which the fly removes particles of dirt adhering to the setae 

 which clothe its body ; the first tarsal joints of the posterior legs 

 are also similarly provided. The tarsi consist of five joints, the 

 terminal joints bearing the " feet." These organs, about which so 

 much has been written, consist of a pair of curved lateral claws or 

 " ungues " which subtend a pair of membranous p3a-iform pads — 

 the pulvilli. The pulvilli are covered on their ventral sides with 

 innumerable, closely-set, secreting hairs by means of which the fly 

 is able to walk in any position on highly polished surfaces. A 

 small sclerite lies between the bases of the pulvilli. The tarsal 

 joints and the other segments of the legs are covered with a large 

 number of setae. 



The Abdomen. 



The abdomen is oviform with the broad end basal. The total 

 number of segments which compose the abdomen is eight in the 

 male and nine in the female. The visible portion consists of 

 apparently four segments in the male and female, in reality there 

 are five, as the first segment has become very much reduced, and 

 has fused with the second abdominal segment forming the anterior 

 face of the base of the abdomen (see fig. 22). The segments 

 succeeding the fifth are greatly reduced in the male, and in the 



