DIPTERA OF MINNESOTA. 



31 



Fig. 13. Central nerv- 

 ous system of Blow 

 Fly, much enlarged. 

 From Lowne. 



What can we say about the sensations of a 

 fly? The sense of smell is evidently located in 

 the antennae, and some believe all over the body. 

 The antennae are likewise apparently the chief 

 organ which has to do with the tactile sense, yet 

 this sense is also without doubt also located 

 over various parts of the body. The auditory 

 sense of a fly is. it is believed, located in certain 

 organs at the base of the halteres, but since in 

 other insects it is thought that certain hairs on 

 the antennae are auditory in function, we must 

 believe that the same is true with flies. The 

 sense of taste in many insects is apparently lo- 

 cated in certain of the mouth parts. 



If a living fly be held by the legs, its wings 

 will vibrate rapidly as in flight, the apex of the 

 wing producing a figure 8 in the air (see Fig. 

 15), the entire wing by its vibrations produc- 

 ing the appearance of a double cone, the apex 

 of wing forming the bases of the two cones, and the shoulder or 

 base of the wing forming the single apex which the two cones have 

 in common. Ordinarily about 330 complete vibrations are made 

 by a fly's wing each second. This rapid movement of the wings 

 produces a buzzing sound, but if the wings are cut ofl^ and the fly 

 held captive, sound is still produced, made in part 

 possibly by air rushing into the spiracles. If, how- 

 ever, the latter are stopped with varnish, we still 

 have a production of sound, which we have reason 

 to believe is made by certain segments of the body 

 moving upon each other, as well as possibly the 

 vibration of the stump of the wing. It will be seen, 

 therefore, that the voice of a fly is quite complicated. 

 The ability of a fly to walk on smooth vertical sur- 

 faces, like glass, or on the ceiling, is not due to 

 suction, but to a secretion on the bottom of the 

 last four tarsal joints. This secretion issues from 

 a large number of hollow pores on each joint and is sufi^ciently ad 

 hesive to support the fly's weight. 



With this brief description of the anatomy of a -fly, we turn at 

 once to a consideration of the families of Minnesota flies, but pre- 



Fig. 14. Thoracic 

 ganglion, much 

 enlarged. After 

 Lowne. 



