SOUNDS OF INSECTS.-VOICE OF VERTEBRATA. 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 Cicadse 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 u 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 Eeptiles 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 
