iv BEUDANT'S EXPERIMENTS 185 



well, and many fishes are known to spend part of 

 their life in each of these media. Direct experi- 

 ments on this matter were made in the beginning of 

 the century by Beudant ; and the results were fully 

 recorded by him in a paper read to the Academy of 

 Sciences. 1 While sudden passage from one medium 

 to another was in most cases conducive to death, he 

 has shown that a gradual passage may be attended 

 with success. A number of Lymnaea, Planorbis, 

 Physa, Ancylus, Paludina^ etc. were divided into two 

 sets ; the one lived in fresh water, the other were put 

 into fresh water to which, every day, a small quantity of 

 salt was added. After a few months, when in the 

 latter case the saltness was 4 / the number of the 

 foregoing individuals which were yet living in the 

 salted water was nearly exactly the same as that of 

 the individuals yet alive in the fresh-water aquarium : 

 in both aquaria the same number of animals had been 

 originally introduced, and out of 400 there remained 

 170 in salt water, 184 in fresh water. 



Other species suffered more ; while only 40 / 

 Paludina died in fresh water, 71*54 % died m sa lt 

 water, and while Unto and Anodonta all throve well 

 in fresh water, they all died in salt. It is an 



1 F. S. Beudant, Memoir c sur la Possibilite de fairs vivre des Mol- 

 lusques fluviatihs dans les Eaux salees, et des Mottusques marins dans 

 les Eaux douces, consideree sous le rapport de la Geologic. Paris, 1816, 

 Journal de Physique, vol. Ixxxiii. p. 268. 



