448 Journal of Coinparathe Neurology and Psychology. 



eral boundary surface of 

 the cloud. This explains 

 the observation often made 

 that Paramecia and other 

 infusoria react and turn 

 away seemingly some dis- 

 tance before reaching the 

 agent causing the reaction. 

 Thus, on approaching a 

 bubble or the free surface 

 of the water, infusoria of- 

 ten react and turn away 

 when still separated by a 

 marked interval from the 

 air surface. A little of the 

 water next to the air has 

 been drawn out to meet the 

 animal, which then reacts 

 to any modification the 

 water may have undergone 

 by contact with the air. 



Thus in its forward 

 course the animal is contin- 

 ually receiving "samples" 



^^S- 3- Spiral course of Para- 

 mecium, showing how the animal 

 is subjected through this method 

 of swimming to man^- changes in 

 its relation to the environment. 

 The arrows at the right indicate 

 some agent (light, gravitation, a 

 water current or the like) acting 

 from a definite direction : the re- 

 lation of the animal to this agent 

 is continually changing ; at b the 

 body is nearly transverse, at d 

 nearly parallel to the arrows. The 

 dotted areas x show the currents 

 of water carried to the anterior end 

 by the movements of the oral cilia. 



