172 THE NEGATIVE GEOTROPISM OF THE PERIWINKLE 



rinsed out and then the experiment was started. The tempera- 

 ture would be changing and the damp conditions would make 

 a specimen alternately dry and wet. It has been shown (Mit- 

 sukuri — 1901), that when a periwinkle, crawling over a dry or 

 moist surface, comes to a pool of water, it almost always pauses 

 and may change direction or cease motion. 



In a general consideration of these results it should be re- 

 membered that the conditions to -which L. lit tore a was subjected 

 in an effort to modify its physiological life history, were condi- 

 tions which would be very often met with in nature without 

 the necessity of radical response. Between spring tides for 

 example, the animals in the low tide level might remain im- 

 mersed for weeks at a time without serious result. The animals 

 used in the immersion experiments were moreover, collected 

 at low tide level. 



