SOUNDS OF INSECTS. VOICE OF VEKTEBRATA. 



517 



much, more delicate nature than the external covering, with a 

 horny plate in the middle, which lies along the bottom. 

 Still more internally are two bun- 

 dles of muscles, which are the real 

 agents in producing the sound ; 

 for, when they are pulled and sud- 

 denly let go, even in a dead speci- 

 men, the sound is produced as 

 well as though the insect were 

 alive. They draw-in and force-out, 

 by their alternate and rapid con- 

 traction, a horny drum or mem- 

 brane, stretched in such a manner 

 as to vibrate readily ; the sound 

 occasioned by the movements of 

 which passes out through an aper- 

 ture resembling the sound-holes 

 of a violin. The Fulgorce, also, 

 have considerable sound-producing 

 powers, but exert them in the 

 night, whilst the Cicadae perform 

 in the day. The Great Lantern- 

 fly of Guiana ( 400, fig. 175) begins regularly at sunset; 

 and its noise, resembling that of a razor-grinder at work, is 

 so loud, that the insect is called " scare-sleep" by the Dutch 

 colonists. 



680. In all air-breathing Vertebrata, the production of 

 sound depends upon the passage of air through a certain, 

 portion of the respiratory tube, which is so constructed as to 

 set the air in vibration. In Reptiles and Mammals, it is at- 

 the point where the windpipe opens into the front of the 

 pharynx, that this vibrating apparatus is situated. Few of 

 the animals of the former class, however, can produce any 

 other sound than a hiss, occasioned by the passage of air 

 through the narrow chink by which the trachea communicates 

 with the pharynx ; but this sound, owing to the great capa- 

 city of their lungs ( 325), is often very much prolonged. 

 Among Mammals, on the other hand, there are few, if any, 

 which have not some vocal sound ; but the variety and 

 expressiveness which can be given to it differ considerably in 

 the several tribes of this class, being by far the greatest in 



Fig. 260. CICADA. 



