536 Natural Hutory of Molluscous Animals : — 



They saw they had no eyes to open, 7 



And that there was no seeing without them !" 



5. Hearing, — If sounds are heard only by such animals 

 as have an organ framed hke the ear, then very few Mollusca 

 can possess this sense ; for traces of an auditory organ, some- 

 what similar to that of fishes, have been detected in the 

 head of the cuttle-fish (Cephalopoda) only, and the organis- 

 ation of it is so imperfect, and its situation so deeply con- 

 cealed, that the impressions received and communicated must 

 necessarily be obscure. All other Mollusca, as I have said, 

 are destitute of organs of hearing, and many of them at least 

 are insensible to sounds. Snails are not affected by loud 

 and harsh noises about them ; nor are the periwinkle and 

 whelk more susceptible in this respect. Baster, however, 

 on the authority of the seamen engaged in carrying muscles 

 to Holland, tells us that these shell-fish are grievously 

 affected by any violent motion and concussion of the air; 

 for if the ship is overtaken by a thunder-storm, or sails too 

 near any other vessel which at the moment discharges its 

 guns, the muscles, frightened with the tremor, shut their 

 valves too suddenly, so as to expel the contained fluid, and in 

 consequence soon die.* It is affirmed also, by Mr. Guilding^ 

 that the (Strombidae possess the sense of hearing, or some- 

 thing allied to it. " I lately suspended," he says, " a num- 

 ber of large ^Strombi by the spire, that the animal when 

 dead might fall from the shell. They had remained in this 

 situation several days, till the body, weak and emaciated, 

 hung down nearly a foot from the aperture, and the eyes 

 had become dim. I found that even before my shadow 

 could pass over them they were aware of my presence, and 

 endeavoured to withdraw into the shell. I then cut off the 

 eyes, with the thick cartilaginous tentacula in which they 

 were lodged, but the animals still continued to be sensible of 

 my near approach, while hanging in this mutilated and pain- 

 ful condition."f The experiment is not conclusive, nor does 

 it appear indeed that any noise was made. The impression 

 which gave the alarm might perhaps be from the pulses of 

 the atmosphere, thrown into motion by the approach of the 

 experimenter, and acting on a skin morbidly sensible. On a 

 summer evening 1 have observed the common spout-fish 

 (6(Men siliqua) extended along the surface of the fine sand in 

 which they burrow, enjoying apparently the calmness and 

 mildness of the season, take alarm and instantaneously de- 

 scend when I was yet distant several yards ; and I can ex- 



* Opusc. Subscciv., i. 109, f Zool. Jouni., iv. 172. 



