MOLLUSCA : THEIE EAES. 65 



who first observed the interesting fact in some speci- 

 mens of the latter which he was keeping in an aqua- 

 rium, says of the sounds, that " they resemble very 

 much the clink of a steel wire on the side of the jar, 

 one stroke only being given at a time, and repeated 

 at intervals of a minute or two ; when placed in a 

 large basin of water the sound is much obscured, 

 and is like that of a watch, one stroke being re- 

 peated, as before, at intervals. The sound is longest 

 and oftenest repeated when the Tritonige are lively and 

 moving about, and is not 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 Tritonise 

 alive in his room for a month, and, duriug 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 audi- 

 ble at the distance of twelve feet. " The sounds obvi- 

 ously 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 her- 

 maphrodites, requiring mutual impregnation, the sounds 

 may possibly be a means of communication between 

 them, or, if they be of an electric nature, they may be 

 the means of defending from foreign enemies one of 

 the most delicate, defenceless, and beautiful Gastero- 

 pods that inliabit the deep." * 



* Edinb. Phil. Joum. xiv. 186. 



