400 F. W. GAMBLE AND FREDEEICK KEEBI.E. 



A 



I 



A 



f 



i 



\ 



B 



Text-fig. 1. — Diagram illustrating the influence of background 

 (white or black) on the movements of Couvoluta roscoff- 

 ensis. 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,. 

 At beginning of experiment, Convoluta fairly uniformly distri- 

 buted. A.,. After forty minutes, Convoluta all on white 

 ground. B. In lateral light (arrows show direction of light). 

 Fifty Convolutas placed in white half of 1, and fifty in black 

 half of 2p I2 and 2^ show the results afi.er two minutes: — 

 in I2 ratio on black and white = f g ; 2o ratio = 5",. Sec 

 text. 



