38 THE HOUSE FLY— DISEASE CARRIER 



(this period increasing in the autumn and being greater 

 also in the springtime), and also upon a period of ten 

 days after emerging of the adult flies before sexual 

 maturity is gained (this point of the duration of the 

 existence of the adult fly before the attainment of sex- 

 ual maturity has been the weak element in other cal- 

 culations that have been made of house fly abundance) 

 — let us start, then, on April 15th with a single over- 

 wintering fly which on that day lays 120 eggs, and we 

 will have the following table: 



April 15th, the over-wintering female fly lays 120 eggs. 



May I St, 120 adults issue, of which 60 are females. 



May loth, 60 females lay 120 eggs each. 



May 28th, 7,200 adults issue, of which 3,600 are females. 



June 8th, 3,600 females lay 120 eggs each. 



June 20th, 432,000 adults issue, of which 216,000 are 



females. 

 June 30th, 216,000 females lay 120 eggs each. 

 July loth, 25.920,000 adults issue, of which 12,960,000 



are females. 

 July 19th, 12,960,000 females lay 120 eggs each. 

 July 29th, 1,555,200,000 adults issue, of which 777,600,000 



are females. 

 August 8th, 777,600,000 females lay 120 eggs each. 

 August i8th, 93,312,000,000 adults issue, of which 46,- 



656,000,000 are females. 

 August 28th, 46,656,000,000 females lay 120 eggs each. 

 September loth, 5,598,720,000,000 adults issue, of which 



one-half are females. 



Such figures as these stagger the imagination. They 

 are apt to make one feel hopeless at the thought of at- 

 tempting to exterminate or to hold in check a creature 



