32 THE HOUSE FLY DISEASE CARRIER 



and he found that after gorging themselves they usually 

 climbed up the sides of the cage and moved from place 

 to place, often stopping to rub one leg against another 

 or to clean themselves by passing the legs over their 

 heads and wings. At intervals he noticed that they 

 sat still and regurgitated large drops of liquid from 

 the tips of their beaks. He showed that the drops 

 gradually enlarged until they were about equal in size 

 to the head of the fly. Sometimes the drop was de- 

 posited, sometimes slowly withdrawn, and this occurred 

 several times. When disturbed, the drops were de- 

 posited or withdrawn with great rapidity. Flies were 

 often seen to suck up the drops deposited by other flies. 

 It is these regurgitated drops which make the larger 

 stains upon a window covered with fly-specks. 



Attention should be called to the shape of the com- 

 pound eyes of the fly, and it will be noticed that they 

 are so situated that a fly can see in all directions at the 

 same time. 



Difference in Size of Adults 



There is a considerable difference in the size of the 

 adult winged flies, but this by no means signifies that 

 small adult flies grow into large ones. This is a wide- 

 spread popular fallacy. The writer once in his younger 

 days attended a meeting of the Philosophical Society 

 of Washington to listen to a paper by the late C. V. 

 Riley on some phases of insect life, in the course of 

 which the house fly was incidentally mentioned. With 

 his entomological training, he was amazed in the dis- 



