200 SENSES HEARING. 



frightened with the tremor, shut their valves too suddenly, 

 so as to expel the contained fluid, and in consequence soon 

 die.* 



Molluscous animals are dumb. There are a very few 

 exceptions. " The noise made by the cuttle-fish, when 

 dragged out of the water, resembles the grunting of a 

 hog." -j- Two nudibranchial Gasteropods have been disco- 

 vered to produce a sound, viz. the Tritonia arborescens 

 and the beautiful Eolis punctata.J The sounds (Fig. 35) 



Fig. 35. 



which the former species produces, when in a glass vessel, 

 says Professor Grant, " 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 

 repeated as before at intervals. The sound is longest and 

 oftenest repeated when the Tritoniae 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 



flass vessel, is mellow and distinct." The Professor has 

 ept 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 diminu- 

 tion of their original intensity. In a still 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 sepa- 

 rate, as if to allow the water to rush into a small vacuum 

 formed within. As these animals are hermaphrodites, re- 



* Opusc. Subseciv. i. 109. t Barbut Gen. Verm. 73. 



t Alder and Hancock Nudibr. Moll. fam. 3, pi. 12. 



