1908. 



NATURAL SCIEXCES OF PHILADELPHIA. 



427 





Fig. 2. (After Willem.) 



Fig. 3. (After Willem.) 



for algae to grow upon and for the snail to "exercise" upon, a structure 

 of microscopic slides of calculated area was introduced. Table V gives 

 the results of these experiments. These results are seen to have little 



Table V — Flat Dish and Jar Area Increased by Slides. 



