414 0. GOEDON HEWITT. 



lialteres are organs of a static function. They are not 

 balancing organs in the sense that they are equivalent to the 

 balancing pole of a rope-walker. They also have probably an 

 auditory function. They are innervated by the largest pair 

 of nerves in the thorax. 



The 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 

 which show any considerable difference in the three pairs of 

 legs. The anterior coxae are comparatively large and boat 

 shaped, the intermediate coxa3 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 pos- 

 terior pair of legs are almost similar to those of the inter- 

 mediate 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 

 succeeding 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 setas 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 pyriform pads the pulvilli. 

 The pulvilli are covered on their ventral sides with innumer- 

 able, 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. 



3. 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 con. 



