ADAPTIVE VARIATIONS. 383 



changes of salinity appears to have been first studied 

 by Beudant * more than eighty years ago. lie placed 

 a number of fresh water molluscs, such as Lymncca^ 

 Planorbis, Pliysa, Ancylus, and Paludina in a vessel of 

 water, and added a small quantity of salt every day. 

 After a few months the water contained 4 per cent, of 

 salt, and 170 of the original 400 molluscs were still sur- 

 viving. Of another 400 kept under otherwise similar 

 conditions in fresh water, 184 were surviving. All 

 species are not equally adaptable, however, as Unio and 

 Anodonta, though they throve well in fresh water, all 

 died in salt. Beudant also performed the converse ex- 

 periment of acclimatising marine molluscs to fresh 

 water. He made observations on 38 different species 

 of the genera H*aliotis, Ceritliium, Buccinum, Tellina, 

 Venus, Ostrea, Pecten, and Mytilus. He added fresh 

 water every day, so that after five months the animals 

 came to live in absolutelv fresh water. Out of the 38 



y 



species experimented with, 20 withstood the change 

 perfectly well. The experiment was started with 610 

 individuals, and of these 375 survived. Of a similar 

 number kept for the same length of time in normal sea 

 water, 401 survived, or only 4.2 per cent. more. How- 

 ever, all the other 18 species experimented with died 

 during the course of the experiment. In still another 

 series of experiments, Beudant succeeded in acclimatis- 

 ing marine molluscs to a solution containing no less than 

 31 per cent, of salts. These consisted chiefly of sodium 

 chloride, but contained also calcium and magnesium 

 chlorides. 



Numerous observations on the acclimatisation of 

 * Journal de Phys., Ixxxiii. p. 268, 1816. 



