THE PHYSIOLOGY OF RESPIRATION IN INSECTS. 385 
per day if all the oxygen is absorbed ; this enables it to perform 
20,000 metre-gramme units of work, or five times the work 
done by man, weight for weight. 
The Work done in Flight.—It is well known that bodies 
falling through the air attain a constant velocity after a certain 
number of seconds, since the resistance of the air increases 
with the square of the velocity. Parachutes attain a constant 
velocity after a short time, which is determined by the resist- 
ance of the air; and it may be experimentally shown that a 
small parachute presenting a surface of 17 square centimetres 
and weighing one gramme, will attain a maximum velocity in 
falling of as nearly as possible one metre per second. As I find 
on measurement that a Cockchafer weighing one gramme has a 
surface of approximately 17 square centimetres when its wings 
and elytra are expanded, its maximum rate of falling may be 
taken as one metre per second. Hence one metre gramme of 
work per second will support it in the air. 
The calculation given in the appendix to this chapter, page 
387, shows that this insect must expend at least 1°33 metre 
grammes of energy per second to attain a velocity of 5 miles 
an hour. It may be objected that insects progress more 
rapidly than 5 miles an hour, but an insect weighing one gramme 
can only do so if it presents a less surface than 7 centimetres 
to the air. I have therefore calculated the maximum velocity 
an insect weighing one gramme could attain if it presented 3 
centimetres of surface to the air. This I find to be=12°5 
metres per second, or 45 kilometres per hour, a trifle over 
25 miles, with an expenditure of 2°2 metre grammes of 
work per second to attain this velocity, which is, I think, the 
highest possible velocity, for an insect of similar weight pre- 
senting its wings almost edge-on to the air; no beetle with 
great elytra could, I think, attain it. 
I believe 7 square centimetres of surface to be a fair estimate 
for the Cockchafer, but with a very small diminution of surface, 
say to 6—and it is impossible to say it cannot expose 6 centi- 
metres—its velocity would be 6°33 metres (nearly), or 22°788 
kilometres per hour (about 13 miles), with an expenditure of 
26—2 
