BY F. ROLAND HAYES, B. SC. 



169 



VI. The Effect of Temperature on Negative Geotropi 



SM 



A series of field observations was initiated at Point Plea- 

 sant Park, Halifax, N. S., on November 28, 1924, with the object 

 of determining the behaviour of Littorina littorea in winter, and 

 of ascertaining if possible, whether a reversal of geotropism 

 occurs during that season. 



To this end a number of one square metre areas were 

 marked out on the shore at typical parts of the intertidal zone 

 and periodical observations made of the changes in their fauna. 

 The varying numbers of L. littorea present on certain of these 

 ai-eas offers a picture of their winter habitat variations. 



Periwinkles virtually disappeared from the upper areas 

 and appeared in constantly increasing numbers just at the 

 lowest tidal level. A table showing the variations in numbers 

 of L. littorea in five areas at low tide level, each of one square 

 metre, is instructive. 



An area is pictured 5 meters long and 1 metre wide, with 

 its greatest length parallel to the shore line, and divided into 

 five one square metre areas. These areas were awash at low 

 tide during neap tides but exposed by the lowest spring tides. 

 Insert 8 point Heading — 



Tai 







AREA 



1 







DATE 



A 



B 



C 



D 



215 



E 



Nov. 28 



155 



170 



135 



180 



Dec. 12 



150 



200 



100 



50 

 205 



50 



Dec. 27 



415 



260 



125 



240 



Mar. 11 



170 



130 



170 



105 



160 



