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 22788 

 kilometres per hour (about 13 miles), with an expenditure of 



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