386 THE TRACHEAL SYSTEM OF THE IMAGO. 
63 metre-grammes of energy per second in its onward pro- 
gression, and of 1°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 Syrphidz and Tabanidz, 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. 
