428 



PROCEEDINGS OF THE ACADEMY OF 



[July, 



Fig. 4. 



significance. In some, however, no slides were used (Table VI). 

 Out of seven experiments but one difference was significant, and that 

 one indicated that the larger surface was beneficial. 



However, these experiments seem to indicate that the effect of sur- 

 face aeration is not very striking, yet increased aeration by the surface 

 of the water no doubt is of slight advantage to the growth of the snail. 



Artificial Aeration. — In a number of experiments streams of air 

 bubbles were conducted through jars of water. The apparatus used 

 was a modification of that of Willem (^96) (see fig. 4). In Experiments 

 37-43 (Table VII) the air was passed through night and day, in the 

 remaining experiments for but eight hours a day. The results confirm 

 Willem's conclusion that cuticular respiration is a large factor in the 

 growth of Lymncea. 



