STRIDULATION OF INSECTS. S6S 



and have pierced and torn them in other instances, without 

 kilhng the insect; but have not observed any thing which 

 would lead to a knowledge of their use. These cavities are 

 not exactly alike in all the locusts. In some species they are 

 true pouches deeply sunk into the abdomen ; in others, not so 

 deeply, and the membrane appears to extend to the surface of 

 the body. This membrane does not seem to be fastened 

 underneath, and may be removed without injury, by cutting 

 the scaly edge to which it is fixed. These cavities exist both 

 in the larvae and pupae ; they are however less developed than 

 in the perfect insects : it would seem that they increase in 

 importance with the age of the animal, and do not attain per- 

 fection till its maturity; from which it would appear that these 

 organs do not completely perform the functions required of 

 them till the insect arrives at this latter period of its life. In 

 order to see them well, it is necessary to examine a large spe- 

 cies such as the migratory locust {Acridium migratorium). 



After the preceding remarks, we are naturally led to reflect, 

 that all the stridulatory insects hitherto mentioned, except 

 the mole-cricket, are provided with an organ, of the functions 

 of which we are entirely ignorant. This organ appears 

 imder the form of a thin transparent plate, with a plane or 

 concave surface. On the other hand, we cannot doubt that 

 these insects have the power of hearing. If it were not so, 

 the females would not be attracted by the song of the males, 

 and the vocal organ would be useless. The organs of hearing 

 and voice, are essentially connected with each other. It does 

 not seem impossible, therefore, that the organs we have had 

 under consideration, are the ears of Orthoptera. The theory 

 of the transmission of sound is not inconsistent with this 

 hypothesis ; for it is admitted that sound is produced by the 

 vibrations of a sonorous body, and that it is transmitted by 

 vibrations of the air excited thereby. In order that these 

 vibrations may convey the perception of sound to an animal, 

 it is requisite that they fall on an elastic membrane, capable of 

 transmitting them to auditory nerves. This condition will be 

 fulfilled, when a microscopic examination shall discover nerves 

 connecting these membranes or organs with the internal gan- 

 glionic system. 



The sub-alary cavity of the locusts much resembles an ear 

 in form ; the cavity seems to be the conch, and the canal 



