436 



PROCEEDINGS OF THE ACADEMY OF 



[July, 



rather suddenly stimulates the snail to become active so as to escape 

 from the cold. The same reaction is noticed when heat above the 

 optimum is applied. (2) When the water continued cold the activities 

 decreased. 



Fig. 5. — Temperature and velocity curve of large and small Lj^fnnsea. [Line 1 1 

 represents temperature in centigrade during three hours. Dotted line rep- 

 resents distance traveled in m.m. in five-minute intervals by the large 

 snails. The solid line shows the same thing for the small ones.] 



The experiments on growth conducted by Semper did not take into 

 account the effect of cold on the water plant. To eUminate this 

 factor the writer alternated the jars wdth the water plant from the 

 warm to the cold at stated intervals, but transferred the snails from 

 one jar to the other, so that certain snails remained in the warm and 

 certain snails remained in the cold all the time, yet the jars that con- 

 tained them were the same, and therefore the amount and condition of 

 the food was similar. 



The manner that cold acts on the growth of Lymncea may be twofold. 

 Cold, as is so well known, retards the rate of chemical combinations and 

 so retards physiological processes. As growth is a physiological 

 process it is retarded, and as the activities of the animal are physio- 

 logical processes they are also retarded. Growth depends largely on the 

 presence of food, yet the food of Lymnaa is acquired only through 

 constant motion, so it might easily become dwarfed, with abundance of 

 food about it, if conditions should make the snail sluggish. In LymncBa 

 we have seen that both these factors may be at work, reduced physio- 

 logical processes acting directly on growth, or reduced activities may 

 actually caus(; dwarfing by lack of food. 



