1 68 ANIMALS 



contains a large calcareous concretion, the ''ear stone," or 

 numerous smaller particles which are called ear sand. 



393. The labyrinth of the round-mouth eels is a simple 

 ovoidal sack, but in the higher fishes the sack is partly divided 

 into two chambers, a utriculus and a saculus, and connecting 

 with the utriculus are three semi-circular canals, two of which 

 are in vertical planes but at right angles to each other, while 

 the third canal is horizontal. 



394. In the higher vertebrates the utriculus with the three 

 semi-circular canals, and the sacculus are also found, and, in 

 essential features, the same as in the higher hshes. 



395. The function of this part of the vertebrate ear is the 

 same as that served by the statocyst of the invertebrates. It 

 has nothing to do with hearing. It is an organ of orientation 

 and equilibration. If the organ is destroyed or the nerve 

 leading to it severed, the animal has difhculty in maintaining 

 its normal upright position. A fish, for example, which has 

 lost the use of this organ no longer swims in its normal way. It 

 turns over and over, or may swim with its back downward. 



396. The Auditory Organ.— The sense of hearing seems to be 

 primarily developed in connection with voice, and it is doubtful 

 whether there is any species in which one occurs without the 

 other. Within the class Insecta we find the only invertebrates 

 having sense organs for the perception of sound, and the species 

 in which they occur best developed are our singing insects, the 

 grasshopper, katydid, cricket, and cicada (''locust," "harvest 

 fly," "jar fly"). The singing in these cases is usually done by 

 the male, and is intended for the "ears" of the female. Many 

 sounds are produced by animals, which are accidental, and can- 

 not be called voice, as in most cases the buzzing produced by 

 the wings in flight. At the same time the buzz of the wings 

 may, in some cases, be used as a means of communication be- 

 tween individuals, in which case it would have to be regarded 

 as voice. On the other hand, sound vibrations may be per- 



