46 



PLANT-ANIMALS 



[CH. 



B 



Fig. 10. Diagram illustrating the influence of background (white 

 or black) on the movements of Convoluta roscoffensis. The 

 animals are placed in shallow porcelain troughs, the bottoms of 

 which are half white and half black (shaded). Each dash 

 represents a Convoluta. A. In uniform light. A t . At beginning 

 of experiment, Convoluta fairly uniformly distributed. A 2 . After 

 forty minutes, Convoluta all on white ground. B. In lateral 

 light (arrows show direction of light). Fifty Convolutas placed 

 in the white half of li, and fifty in the black half of 2 X . 1 2 and 2 2 

 show the results after two minutes : in 1 2 ratio on black and 

 white = f ; in 2 2 ratio = -fo . See text. 



