100 Herbert Eugene Walter 



bring them into the plane of the floor. The course taken by a 

 planarian is indicated by the tortuous hne. The full line shows 

 the course taken on the solid surface of the aquarium; the dot- 



Fig, lo Dendrocoelum lacteum. The shortness of the path shows comparatively little persistence 

 in locomotion, and the direction, considerable indifference to the source of light. 



and-dash lines, the course of the worm on the surface film. The 

 dotted line indicates a hiatus in the path, made necessary by the 

 attempt to represent on a flat surface a continuous line which tra- 

 verses vertical as well as horizontal surfaces. A succession of 



