PRODUCTION OF SOUNDS BY ANIMALS. 
513 
(fig. 255). A similar tail is possessed by some of the Opos¬ 
sum tribe; and by the Chameleon among Eeptiles. 
CHAPTEE XIII. 
OF THE PRODUCTION OF SOUNDS : VOICE AND SPEECH. 
675. It is not by their movements alone, that Animals are 
enabled to influence one another. Were it so, their commu¬ 
nication would be restricted to the small amount which can 
be effected by signs and gestures. This, however, is necessa¬ 
rily the case amongst aquatic animals in general; since they 
are prevented by the nature of the medium they breathe 
from producing sounds through its means. Some of them 
appear to have the power of communicating with each 
other by the vibrations which they can excite in the water; 
of this we have already noticed an example among the 
Whale tribe (§ 491); and there is reason to believe that certain 
Mollusks possess a similar means of communication. 
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