388 PHYSIOLOGY. 



were in vain, for its clipped wings made flight impossible. 

 which are held by the wings behind, may be very well examined, and 

 the pulsations of the abdomen are very distinct, but no motion is to be 

 detected in the thorax. The number of these pulsations* is greater than 

 in the cockchafer, but not so'great as in the green locust. I estimate 

 them at from thirty to thirty-five in a minute. I consider, besides, 

 that the pulsations increase when the voluntary motions, for instance, 

 that of flight, are in exercise, which I conclude from the respiration of 

 a LibeHula held in the above manner, increasing upon its endeavours 

 to free itself. During this, however, the spiracles of the abdomen did 

 not appear to inspire, and the contractions of the abdomen recommenced 

 only after the motion of the thorax. Treviranus * concluded, from 

 similar observations, and, indeed, justly, that the spiracles of the 

 abdomen respire during repose, whereas those of the thorax are especially 

 in action during flight. He cites as a proof, that the same muscles 

 which contract the cavity of the thorax, our straight dorsal and pectoral 

 muscles as well as the oblique lateral and dorso-lateral muscles, effect 

 the first expansion of the wings by the general contraction of the thorax, 

 and, subsequently, in conjunction with the true alary muscles, produce 

 the motion of flight by the alternating distension and contraction of 

 the thorax. During this motion of the thorax, air must necessarily 

 pour in and out, particularly as the expiration of the abdomen pro- 

 gressively increases, as is proved by my observations upon the cockchafer, 

 and the deeper it becomes, the earlier do the spiracles of the thorax 

 commence breathing, and this supposition is strongly supported by the 

 motion of the head and prothorax. At the verv moment, however, that 

 the beetle flies off, it compresses its xvhole abdomen together, and this 

 is continued during its whole flight, a clear proof that the whole function 

 of respiration now is effected by the spiracles of the thorax. We may 

 also note that the sudden breathing of the abdomen in insects upon their 

 settling after flight, namely, in the flies, bees, and wasps, tends to 

 support it. The longer the creature reposes, the slower and more 

 regular the pulsations of the abdomen become. This opinion also of 

 the respiration through the spiracles of the thorax gives a sufficient 

 explanation of the humming noises produced by most insects during 

 flight, as I shall prove in detail below, for it cannot be conceived that 

 the mere flapping of the wing can produce it, but that it proceeds 



* Das organische Leben, t. i. p. 262. 



