'Pond-snails 



313 



of eggs, and rearing them in volumes of water 

 varying from 100 to 2000 cubic centimetres, with 

 a full supply of food in each, and all other condi- 

 tions equal and as natural as possible. At the end 

 of sixty-five days those specimens reared in the 

 maximum amount of water were just three times 

 the leno^th of those in the minimum volume, and 

 the intermediate ones in proportion. Its eggs are 

 deposited in almost cylindrical masses, often curved, 



Great PonH-sna 



containing from 50 to 120 eggs. Half-grown 

 specimens are much more slender than the adults, 

 the shell nearly transparent, and the mouth con- 

 tracted. The Great Pond-snail may be found in 

 still or slow waters throughout the country. 



The Marsh Limnsea {L. iKdustris) has a more 

 solid shell, but its body-whorl is not nearly so 

 swollen in proportion, so that the length and breadth 

 measurements are as 5 to 2. The shell is dull 



