From National Geographic Magazine. Washington, D. C. Copyright, igio, ali 

 rights reserved. 



(1) Adult house-fly from above. 

 (After Cobb.) 



From National Geographic Magazine. Washington, D.C. Copyright, JQIO, all 

 rights reserved. 



(2) Adult house-fly from below. 

 (After Cobb.) 



[Frontispiece 



