56 EVENINGS AT THE MICROSCOPE. 



ordinary evolutions. They constantly keep up a series of 

 swinging or balancing movements, sometimes rotating, 

 sometimes forcibly driven in a certain direction, then in 

 the opposite, yet no single one ever by any accident 

 touching the walls of the capsule in which they are con- 

 tained. If the capsule be ruptured, the motions instantly 

 cease. These little bodies are of a calcareous nature ; 

 and they are called otolithes* that is, ear- stones. The 

 most that we know of these curious capsules, which 

 are indubitably ascertained to be organs of hearing, we 

 owe to the observations of the eminent zoologist just 

 named, and of this you may perhaps like to learn a 

 little. 



Siebold says that a concentric depression is evident in 

 these otolithes, and that there may be seen in the centre 

 of the greater number of them a shaded spot, or rather a 

 minute aperture, which penetrates through the concretion 

 from the one flattened surface to the other. Subjected to 

 a strong pressure, the otolithes crack in radiating lines, 

 separating often into four pyramidal pieces. This separa- 

 tion also ensues, after a longer time, when the otolithes 

 are immersed in diluted nitric acid; and, if we touch them 

 with the concentrated acid, they suddenly dissolve with 

 the disengagement of a gas, whence Siebold concludes 

 them to be composed of carbonate of lime. The size of 

 the otolithes is not equal, and in the same capsule there 

 are always some which are smaller than others. Within 

 the capsule they have, during life, a very remarkable, and 

 in some respects peculiar, lively, oscillatory movement, 

 being driven about as particles of any light insoluble 

 powder might be in boiling water. The otolithes in the 

 centre have the appearance of being pressed together so 

 as to form a sort of solid nucleus, and towards this centre 

 the otolithes near the circumference seem even to be 



* From the Greek ovg (ous), genitive Cjtoq (otos), an ear, and \i6oq 

 (lithos), a stone. 



