64 EVENINGS AT THE MICEOSCOPE. 



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 towards the circumference seem even to 

 be violently urged, their centripetal rush being invari- 

 ably repulsed, and as often driven again into a centri- 

 fugal direction. Removed from the capsule, the mo- 

 tions of the otolithes instantly cease. The cause of 

 these curious oscillations remain undiscovered. Siebold 

 could detect no vibratile cilia on the surfaces of the 

 capsule, and the cessation of the motion when the oto- 

 lithes are removed, proves them to be unciliated them- 

 selves, and, at the same time, distinguishes the motion 

 from that of inorganic molecules. 



It has been more recently ascertained that the move- 

 ments of the otolithes are due to very minute cilia with 

 which the interior surface of the capsule is covered. 

 This had been long suspected, and some eminent physi- 

 ologists, as "Wagner and Kolliker, have distinctly seen 

 the cilia themselves. 



If you ask what can be the use of ears to a class of 

 animals which are invariably dumb, I answer that 

 though this is true with respect to the great majority, 

 yet it may be only that our senses are too dull to per- 

 ceive the delicate sounds which they utter, and which 

 may be sufficiently audible to their more sensitive or- 

 gans ; and besides, some IMEollusca can certainly emit 

 sounds audible to us. Two very elegant species of Sea- 

 slug, viz. JEolis punctata, and Tritonia arborescens,* 

 certainly produce audible sounds. Professor Grant, 



* Now called Dendronotus arhorescens. 



