BY F. ROLAND HAYES, B. SC. 



161 



III, Correlation of Negative Geotropism with Vertical 



Habitat 



In Table 1 will be found the figures representing the aver- 

 age responses of animals collected at low, mid and high tide 

 levels. 



The results for both "immersed" and "dry" groups are 

 given. All the animals used were collected immediately be- 

 fore the commencement of the experiment. 



Table I 



TIDAL 

 LEVEL 



"IMMERSED" GROUP 



RESPONSE PER ANIMAL 



PER TEN MINUTES 



CENTIMETERS 



"DRY" GROUP 



RESPONSE PER ANIMAL 



PER TEN MINUTES 



CENTIMETERS 



Low 



Mid 



High 



14.6 

 21.0 

 26.7 



3.6 

 19.0 



12.6 



This table indicates that a physiological gradient exists in 

 L. littorea correlated with its position in the littoral zone^ and 

 that the negative geotropic response may serve as an index to 

 this gradient. A further discussion of these results will be 

 found at the close of this paper. 



