j-jo THE ANIMAL KINGDOM. 



sides of their bodies, which receive air from outside by 

 means of breathing pores (spiracles}. These air-tubes 

 divide internally into innumerable branches, and thus 

 carry the air into every part of the system. There is a 

 marvellous arrangement in connection with them, which 

 I must not omit to mention to you namely, the means 

 by which these minute channels are kept open. You 

 must know that each of the tubes is made of two distinct 

 layers of delicate membrane ; well, between these a fine 

 thread, finer than you can possibly imagine, is coiled 

 round and round throughout the whole length, just as fine 

 wire is coiled inside india-rubber tubing, to prevent its 

 sides becoming pressed together. By this means, not 

 only is the insect well supplied with air, and thus 

 lightened, but by breathing in every part, its vitality that 

 is, its powers of life is increased, so that it is, in 

 proportion to its bulk, the strongest of living things. 

 Professor Rymer Jones says, " A common flea or grass- 

 hopper will spring two hundred times the length of its 

 body," which is as though a man could at a single bound 

 leap over the ball and cross of St. Paul's Cathedral. It 

 has been calculated that in its ordinary flight the common 

 house-fly makes with its wings about six hundred strokes 

 in each second of time, which will carry it about five feet ; 

 but this speed can be increased to from thirty to thirty-five 

 feet in a second, Now in this space of time a race- 

 horse could only clear ninety feet, which is at the rate 

 of more than a mile in a minute ; so that when you are 

 told that 10,000,000 of the fly would hardly weigh as much 

 as the race-horse, you will see how wonderful is the speed 

 of the comparatively tiny creature. 



Fancy if the fly were increased in size until it equalled 

 the race-horse, and its powers of flying increased in equal 

 ratio, how great would be the speed at which it would be 

 able to travel 1 



