58 EVENINGS AT THE MICROSCOPE. 



heard when they are cold and without any motion ; in the 

 dark I have not observed any light emitted at the time of 

 the stroke ; no globule of air escapes to the surface of the 

 water, nor is any ripple produced on the surface at the 

 instant of the stroke ; the sound, when in a glass vessel, is 

 mellow and distinct." The Professor has kept these 

 Tritoniae alive in his room for a month, and during the 

 whole period of their confinement they have continued to 

 produce the sounds with very little diminution of their 

 original intensity. In a small apartment they are audible 

 at the distance of twelve feet. " The sounds obviously 

 proceed from the mouth of the animal ; and at the instant 

 of the stroke, we observe the lips suddenly separate, as if 

 to allow the water to rush into a small vacuum formed 

 within. As these animals are hermaphrodites, requiring 

 mutual impregnation, the sounds may possibly be a means 

 of communication between them ; or, if they are of an 

 electric nature, they may be the means of defending from 

 foreign enemies one of the most delicate, defenceless, and 

 beautiful Gasteropods that inhabit the deep."* 



* Edinb. Phil. Journ., xiv. 186. 



