THE TYPHOID FLY 



143 



ering in these somewhat circumscribed settlements or " locations," they 

 gave the impression that they were more numerous this year than last. 

 In the sense that their numbers were more concentrated, owing to the 

 limitation of moisture — a prime necessity in the life of a fly — this is 

 probably true. 



It may be of interest to consider some statistics, showing to what 

 enormous numbers the descendants of one fly may reach in the course 

 of a summer. As most of you are aware, the eggs of a house fly hatch 

 in from approximately six to twelve hours, and the maggots issuing 

 therefrom reach their full size in from four to seven days. The outer 

 layers of their body then harden and turn brown, forming the pu- 

 parium, while the parts within become what is known as the pupa. 

 The duration of the pupal stage is from five to seven days, at the 

 expiration of which time the adult emerges as a perfect fly. The life 

 of the house fly then occupies from ten to twelve days, and there may 

 be from ten to thirteen or more generations in a summer, depending 

 upon the character of the season and on the latitude. Of the length 

 of life of the adult we can not speak with certainty, for the only way 

 this could be determined is by confining the insects, and when this is 

 done, conditions of existence are so unnatural that observations upon 

 this point are not reliable. A female house fly which has hibernated 



The Unsanitary Condition of the Rear End of a Restaurant off from an Alley. 



