THE PLY, 49 



he states, "their velocity can be increased six- or 

 seven-fold, or to 30 or 35 feet per second. In this space 

 of time a race-horse would clear oiolj 90 feet, which is 

 at the rate of more than a mUe per minute. Our little 

 My, in her swiftest flight, wiU in the same space of 

 time go more than the third of a mile. Now, compare 

 the iufinite difference of the size of the two animals 

 (ten millions of the Fly would hardly couaterpoise one 

 racer), and how wonderful wiU the velocity of the 

 nunute creature appear ! Did the My equal the race- 

 horse in size, and retain its present powers in the ratio 

 of its magnitude, it would traverse the globe with the 

 rapidity of lightning ! " 



Every observer must have remarked with what ease 

 the fly plays around the head of a horse in rapid 

 motion ; and Vogt says the Gad-fly flies with a speed 

 equal to that of a railway-traiu. Though this may ap- 

 pear exaggerated, the calculation wiU. not seem so far 

 from the truth, when we notice that, whilst the moving 

 body proceeds in straight lines, the insect performs 

 numerous gyrations at the same time, thereby con- 

 siderably iucreasiug the distance. Some allowance 

 must be made for the assistance the insect derives 

 from the stratum of air put in motion by the pro- 

 gression of the object, as also by the momentum 

 gained by occasionally touching the object with which 

 it is traveUing. The common Gnat {Culex pipiens) 

 has a much higher rate of vibrations, which are com- 

 puted at many thousands per second. 

 ' In such insects as possess two pairs of wings, e. g. 



D 



