THE HOUSE-FLY 71 



in the air, and fly with equal facility and 

 swiftness backwards or forwards, to the right 

 or to the left, without turning. The same 

 writer asks us to suppose for a moment that 

 the law which restricts the dimensions of an 

 insect could be dispensed with in a single 

 species. Suppose a wasp or a stag-beetle 

 dilated to the bulk of a tiger or of an 

 elephant cased in impenetrable armour, fur- 

 nished with jaws that would crush the solid 

 trunk of an oak winged and capable of flight 

 so rapid as to render escape hopeless what 

 could resist such destroyers? Or how would 

 the world support their ravages ? With 

 regard to the house-fly (Musca domestica), 

 Bymer Jones quotes an anonymous writer 

 who has calculated the flight of this insect : 

 ' In ordinary flight it makes with its wings 

 about 600 strokes, which carry it 5 feet, every 

 second; but if alarmed their velocity can be 

 increased six or sevenfold, or to 30 or 35 feet 

 in the same period! In this space of time an 

 Arab steed would clear only 90 feet, which is 

 at the rate of more than a mile a minute. 



