A B 



III EFFECT OF VOLUME OF WATER 95 



known optimum. He found, in the result, that the size of the 

 shell varied directly in proportion to the volume of the water in 

 which it lived, and that this was the case, whether an individual 

 specimen was kept alone in a given quantity of water, or shared 

 it with several others. At the close of 65 days the specimens 

 raised in 1 00 cubic cm. of water were only 

 6 mm. long, those in 250 cubic cm. were 

 9 mm. long, those in 600 cubic cm. were 

 12 mm. long, while those kept in 2000 

 cubic cm. attained a length of 18 mm. 



(Fig. 37). FiQ. 37. _ Four equally old 



An interesting effect of a sudden fall shells of Limnaea stag- 



- . . j^- 1 1 o • nalis, hatched from the 



of temperature was noticed by Semper m game mass of ova, but 

 connection with the above experiments. reared in different voi- 



-rr 1 c 1 • , • • • umes of water: A in 100, 



Vessels 01 unequal size, containing speci- b in 250, c in 600, and D 

 mens of the Limnaea, happened to stand ^ 2000 cubic centime- 



, » . T , . • 1 . 1 i tres. (After K. Semper.) 



before a window at a time when the tem- 

 perature suddenly fell to about 55° F. The sun, which shone 

 through the window, warmed the water in the smaller vessels, 

 but had no effect upon the temperature of the larger. The 

 result was, that the Limnaea in 2000 cubic cm., which ought 

 to have been 10 mm. long when 25 days old, were scarcely 

 longer, at the end of that period, than those which had lived in 

 the smaller vessels, but whose water had been sufficiently warm. 



