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." f Two nudibranchial Gasteropods have been disco- 

 vered to produce a sound, viz. the Tritonia arborescens 

 and the beautiful Eolis punctata.]: The sounds (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 w^atch, one stroke being 

 repeated as before at intervals. The sound is longest and 

 oftenest repeated when the Tritonia; are lively and moving 

 about, and is not heard when they are cold and without any 

 motion; in the dark 1 have not observed any light enutted 

 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 Tritoniai alive in his room for a month, and, 

 during the whole period of their confinement, they iiave 

 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. 



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



