MOLLUSCA : TUEIK EAES. 63 



doep-seated in the soft flesh, a pair of perfectly trans- 

 parent globules, or bladders, -without any opening, but 

 filled with a clear fluitl, in which there are some minute 

 bodies performing the most extraordinary evolutions. 

 Tliey constantly keep up a scries of swinging or balanc- 

 ing 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 contained. If the cap- 

 sule be ruptured, the motions instantly cease. Tliese 

 little bodies are of a calcareous nature ; and they are 

 called otolithes^ that is, ear-stones. Tlie most that we 

 know of these curious capsuleSj which are indubitably 

 ascertained to be organs of hearing, we owe to the ob- 

 servations of the eminent zoologist just named, and you 

 may perhaps like to know a little more about them. 



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 pyra- 

 midal pieces. This separation 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 



