6 



weeks according to temperature. At the time of pupation 

 it is 6 to 9 mm. in length. Pupation lasts from five days to 

 a month according to temperature. Thus the whole cycle, 

 from laying of egg to emergence of the fly, occupies from 

 ten days to two months, according as the weather be warm 

 or cool. Shortly after emergence from the chrysalis the young 

 fly spreads its wings, which soon harden, and flies away in 

 search of food. The young female is ready to lay its first 

 batch of eggs in about ten days, or even sooner in warm 

 weather. 2 During winter a few flies survive in warm and 

 secluded places. In the spring these start the next year's 

 supply. The possible progeny of one female fly from April 

 to September have been estimated at 10 13 . Howard, of the 

 United States Department of Agriculture, estimates that in 

 40 days the descendants of the fly might number 12 millions, 

 or 800 Ib. weight. 



Structure and Habits. 



The only points in the structure of the fly it is essential to 

 direct your attention to are the legs and feet and the general 

 arrangement of the alimentary apparatus. These will be 

 sufficiently obvious in the diagrams. (Figs. 2 and 3.) Please 



A leg and foot of a fly. 



note that the feet are covered with minute hairs. They are, 

 indeed, more numerous and finer than in the diagram, and 

 extremely fine ones are also placed upon the pads (these are 

 stated to secrete a sticky substance by means of which the 

 fly grips), the basal part of the claws, and the distal stiff 

 hair which projects from the end of the last joint of the 

 tarsus. (Fig. 2.) Each leg is like a minute paint brush, 

 which is applied to the surface of whatever it rests upon. 

 When this is water the hairs do not appear to be wetted. 



The essential parts of the alimentary canal are a gullet, 

 stomach, crop, intestine, and rectum. (Fig. 3.) The 

 gullet is prolonged to a minute opening between the 



2 No doubt the cycle may be much shorter or longer under a wider 

 range of temperature than that from which these records have been 

 taken. 



