112 Natural History of Molluscous Animals : — 



explain, in some degree, the apparent apathy of the Mollusca 

 generally to a temporary deprivation of their respiratory 

 media : for snails may be immersed in water for many hours 

 without injury; and the purely aquatic species will survive as 

 long a time exposed to the atmosphere. Oysters and muscles, 

 as every one knows, and probably all the Conchifera, will 

 live for three or four days without any more water to breathe 

 in than what may lie in the concavity of their shells ; and 

 Mr. Boyle has some experiments which illustrate, in a remark- 

 able manner, their tenacity of life even in vacuum. He found 

 that two oysters, put " into a very small receiver," exhausted 

 of air, were alive at the end of twenty-four hours ; " but how 

 long afterwards they continued so, I did not observe." {Phil. 

 Trans., 1670, p. 2023.) Another oyster was put into a vial 

 full of water before being enclosed in the receiver, " that, 

 through the liquor, the motion of the (air) bubbles, expected 

 from the fish, might be more pleasantly seen and considered. 

 This oyster proved so strong, as to keep itself close shut, and 

 repressed the eruption of the bubbles, that in the other did 

 force open the shells from time to time ; and kept in its own 

 air as long as we had occasion to continue the trials." {Ibid., 

 p. 2024.) Shelled snails (Helices) appeared to be not more 

 disordered in vacuity ; and even the slugs (Z>imax) endured 

 the privation for many hours. The same illustrious philo- 

 sopher included two of the latter " in a small portable 

 receiver," carefully exhausted ; " but, though they did not 

 lose their motion near so soon as other animals were in 

 our vacuum wont to do, yet, coming to look on them after 

 some hours, they appeared moveless and very tumid; and, at 

 the end of twelve hours, the inward parts of their bodies 

 seemed to be almost vanished, and they seemed to be but a 

 couple of small full-blown bladders ; and, on the letting in of 

 the air, they immediately so shrunk, as if the bladders had 

 been pricked : the receding air had left behind it nothing but 

 skins ; nor did either of the snails afterwards, though kept 

 many hours, give any signs of life." {Ibid., p. 2050.) In this 

 experiment, it is obvious that the snails were killed from the 

 mechanical effects of the expansion of the air within them, 

 and not from its ingress to the pulmonary cavity being 

 prevented. 



which were even kept close in salt water, seemed to have the power of 

 purifying it, and rendering it fit for respiration; while many large air- 

 bubbles were generated in the glass. Some power of this kind would be 

 very valuable to those species which inhabit maritime ponds, the waters of 

 which, nearly dried up at certain seasons, must be stagnant and unwhole- 

 some." (Zoological Journal^ vol. v. p. 33.) 



