THE VOICE AND SPEECH. 649 
etc., take part. Most reptiles are voiceless, in the proper sense, 
though there are few that can not produce a sort of hissing 
sound, caused by the forcible emission of air through the upper 
respiratory passages. 
Frogs, as is well known, produce sounds of great variety in 
pitch, quality, and intensity, some species croaking so as to be 
heard at the distance of at least a 
mile. It is a matter of easy ob- 
servation that when frogs croak 
the capacity of the mouth cavity 
is greatly increased, owing to dis- D 
tention of resonating sacs situated 
at each angle of the jaws. When 
tree-frogs croak, their throats are 
greatly distended, apparently in 
successive waves. But itis among 
insects that the greatest variety 
of methods of producing’ sounds is 
found. 
In bees and flies sounds are 
caused by the vibration of mus- 
cular reeds placed in the stigmata 
or openings of their tracheal tubes, 
also by the extremely rapid vibra- 
tion of their wings. The death- 
head moth is said to force air from 
its sucking stomach, and thus give Ti, 00, — erties OF. trgehca.or atr-tibe 
rise to a sound in the same way a. epitheliallike cellular fayer ; b, 
as certain fishes. Fept up by colled chitinows bes, 
In the grasshopper a noise is vessels. pfanatiaalaypenebalserery 
produced by rubbing its rough sitiaeiaiis 
legs against the wing-cases, and in allied forms (locusts) by 
moving the wing-cases against one another ; and in other groups 
different parts of the body are brought into mutual contact or 
rubbed or struck against foreign bodies. 
SF 
pom 
)) Tig 
i 
SPEECH. 
It may be noticed that the differences of voices, by which 
we are enabled to discriminate between individuals, are much 
more marked during speaking than singing. This is owing to 
greater prominence of over-tones in the speaking voice, as may 
be readily shown. 
