THE NEGATIVE GEOTROPISM OF THE PERIWINKLE 165 



From these figures it can be clearly seen that longer periods 

 of desiccation result in a well defined decrease in amount of 

 response and percentage of animals showing activity. No 

 other results could be in accordance with the facts observable 

 through a study of the natural history of the species. If, in 

 nature the animals continued to walk uphill after they had 

 been subjected to intertidal exposure for a few hours, they would 

 clearly soon migrate out of the littoral zone and become subject 

 to conditions which must finally prove to be lethal. 



The figures for several of the latter readings are based on 

 the performance of so few individuals that they do not form as 

 exact a mathematical gradient as might have been desired, but 

 the general trend of the results is very clearly definable. 



In order to test whether the results of this series of experi- 

 ments might not be due to starvation rather than to desiccation, 

 animals which had been desiccated for varying periods of time 

 were subjected to a simple test. 



They were first regularly tested and then placed in a jar 

 heaving the mouth covered by wire gauze, which permitted the 

 passage of sea water but not of the algae which serves as food, 

 and suspended in the sea for twenty-four hours; they were 

 then tested again. The results showed conclusively that the 

 effects were from desiccation and not starvation. 



Apparently metabolic activity decreases greatly when 

 the animals seal themselves up during periods of drought. 



Table 4 furnishes two examples which will suff"ice as illus- 

 tration. 



