78 THE HOUSE-FLY 



ing obnoxious substances which might be 

 productive of zymotic and other diseases. It 

 is also evident that if we were to keep our 

 homes absolutely free from all impurities we 

 should not be so much troubled by these 

 visitors. House-flies will not remain long in a 

 house that has nothing for them to feed on. 

 On referring to the illustration (Fig. 18), 

 some 21 or 22 eggs of the fly will be seen. 

 They are objects of great beauty under the 

 microscope. The original photo-micrograph is 

 one of 72 diameters ; the time of exposure was 

 60 minutes ; the focal distance 60 inches, and 

 the objective used the inch. 



