Couriers of the Air. 79 



mechanism the creature pursues its prey of 

 smaller insects with such rapidity. 



There are many insects which one would little 

 suspect being furnished with apparatus suited to 

 swift and more or less continuous flight. House 

 flies frequent the insides of our windows, buzzing 

 sluggishly in and out of the room. But what 

 different creatures are they when they accom- 

 pany your horse on a hot summer's day. A 

 swarm of these little pests keep pertinaciously 

 on wing about the horse's ears ; quicken the 

 pace up to ten or twelve miles an hour, still they 

 are there ; let a gust of wind arise and carry 

 them backwards and behind, the breeze having 

 dropped, their speed is redoubled, and they 

 return to their post of annoyance to the poor 

 horse, even when urged to its fastest pace. But 

 this example gives only a partial proof of the fly's 

 power of flight, as the following will show. The 

 writer was travelling one day in autumn by rail 

 at about twenty-five miles an hour, when a com- 

 pany of flies put in an appearance at the carriage 

 window. They never settled, but easily kept 

 pace with the train ; so much so, indeed, that 

 their flight seemed to be almost mechanical, and 

 a thought struck the writer that they had pro- 

 bably been drawn into a kind of vortex, whereby 

 they were carried onward with little exertion on 

 the part of themselves. But this notion was 

 quickly dispelled. They sallied forth at right- 



