STRIDULATION OF INSECTS. 371 



each side of the abdomen, on the first and second segment, a 

 double cavity ; the first, that of the first segment, is formed of 

 a smooth transparent membrane, analogous to the drum of the* 

 Cicndcv ; the second is lined with a soft membrane covered 

 with a silky down ; the insect has the power of opening and 

 shutting it at will. When the insect cries it opens, and a long 

 bundle of hair is seen to protrude, w^hich is raised up and ex- 

 pands into a cone-like form : the hairs of which it is composed 

 have a whirling motion ; these hairs have their origin in the 

 superior part of the cavity of the first segment, and when they 

 are at rest exactly hide the two cavities, and are concealed 

 themselves. One can hardly, at the first sight, avoid coming 

 to the conclusion that the cavities, the bundles of hair, and the 

 rotatory movement, are all intimately connected with the emis- 

 sion of the cries uttered by this insect. But how is the sound 

 formed ? The manner of its formation is not apparent. In 

 order to discover it, I raised the scaly plate of the abdo- 

 men, which corresponds to the cavities, and having removed 

 the white and unctuous covering from underneath, laid it 

 bare without injuring it; I then perceived a large white 

 muscle, analogous to those which move the wings of flies ; this 

 muscle terminates in the borders of the cavity of the first seg- 

 ment, and most probably performs an important part in the 

 production of sound. On examining the membrane with the 

 magnifying glass, I could not discover any orifice in the cavities 

 which would allow the passage of air ; thus M. Larey's opinion 

 on this subject, which supposes a rapid emission of air from 

 these cavities, would appear to be without foundation : his 

 conjecture was occasioned by observing the motion of the hairs 

 of which I have spoken. As I held the cartilaginous plate in 

 my fingers with the inner surface uppermost, in order to ex- 

 amine it, I happened to move it, and immediately heard a 

 slight sound, of which I afterwards produced a repetition a 

 number of times, by moving it as if to break it ; I then per- 

 ceived that this noise was referrible to the cavity of the first 

 segment, which altered in form, becoming convex : I consi- 

 der, therefore, that, in all probability, the mechanism of 

 stridulation is produced by the muscle, the effect of which is 

 to render the sonorous organ alternately convex and concave. 

 It would appear, therefore, that there is an analogy between 

 the musical instruments of this insect and those of the Cicadcc. 



