152 THE PHILOSOPHY 



proprietor is abroad in queft of materials to finifli the neft, a 

 ftranger takes poffeffion. At meeting, a battle always en- 

 fues. This battle is fought in the air. Sometimes they fly 

 with fuch rapidity and force againft each other, that both 

 parties fall to the ground. But, in general, like birds of 

 prey, the one endeavours to rife above the other, and to 

 give a downward blow. To avoid the ftroke, the under- 

 moft, inftead of flying forward or laterally, Is frequently ob- 

 ferved to fly backward. This retrograde flight is likevvife 

 performed occafionally by the common houfe-fly, and feme 

 other infers, though we are unable to perceive what fl:imu- 

 lates them to employ this uncommon movement. 



