386 THE TRACHEAL SYSTEM OF THE IMAGO. 



63 metre-grammes of energy per second in its onward pro- 

 gression, and of i '63 in total energy of flight. Such a rate of 

 motion if possible is clearly exceptional. 



In conclusion, I would observe that the rate of flight in 

 the Cockchafer is undoubtedly between 5 and 13 miles an hour, 

 with a total expenditure of energy of from 1*33 to 1*63 metre 

 gramme units of energy per second. If we take the mean 

 as 1*4, and multiply by 3,600, we have 5,800 units per 

 hour, so that in two hours the insect would expend consider- 

 ably more than half its daily store of energy. As these insects 

 are, however, very quiet during the greater part of the day, 

 and only fly for about two hours in the evening, the remain- 

 ing store of energy may suffice, but it is only on the supposition 

 that all the oxygen inspired is absorbed that it is possible to 

 account for the energy manifested. 



The great strength of insects is well known. It is said that 

 some insects can drag sixty-seven times their body weight, whilst 

 a horse can scarcely drag three times its body weight; but such 

 exertion is probably quite exceptional, and its duration short, so 

 that such feats of strength only show that stored energy can 

 be rapidly liberated. 



The high velocities attained by many insects indicate more 

 active respiration, and a proportionately small surface exposed 

 in rapid progression with a large surface to counteract the 

 effect of gravity, and a very light weight. Many insects can 

 undoubtedly progress through the air with a velocity of con- 

 siderably more than 30 miles an hour, and there are none 

 which appear to have an organization better adapted for rapid 

 flight than the Dragon-flies, Hymenoptera and Hawk-moths, 

 which are well known to be extremely rapid fliers. Many of 

 the Syrphidae and Tabanidse, amongst the Diptera, are equally 

 rapid fliers, and their flight is usually sustained for compara- 

 tively long periods. As I have already stated, however, their 

 respiration is exceedingly active, and they exhibit all the 

 conditions necessary for the attainment of a high velocity 

 with a small expenditure of energy. 



