148 The Animal Mind 



colored light while its response to white light remained 

 unchanged. When placed in diluted sea water, the animal 

 would, after a day, direct itself toward violet rays, although 

 still negative in response to white light. On the fourth 

 day the ordinary " chromotropism " was restored; that is, 

 the worm sought red rays. After two or three weeks of 

 life in the diluted sea water, on being restored to ordinary 

 sea water the worm again showed inverted chromotropism, 

 becoming " positive " to the violet rays, while still " nega- 

 tive " to white light. Moreover, intermediate stages in the 

 passage from the red- to the violet-seeking phase were ob- 

 served ; a stage where, still positive to red, the animal ceased 

 to distinguish red from yellow, and others where it sought 

 violet, but had become indifferent to green and yellow. 

 These stages lasted for several hours, but corresponding 

 ones were not observed during the passage from the violet 

 phase back to the red phase : perhaps they occurred too 

 rapidly to be noted (493). 



Hess (314), on the other hand, concludes the total color- 

 blindness of the marine worm Serpula from the fact that 

 when tested by the direction in which it turned when sub- 

 jected to light passing through differently colored glass, it 

 showed evidence that the yellow-green had most effect, 

 and that the effectiveness diminished rapidly towards red, 

 slowly towards violet : in other words, that the brightness 

 effect of the colors was like that shown in the case of a 

 color-blind human being. 



Hess (306) also studied the comparative effectiveness of dif- 

 ferent colored rays on the eyes of cephalopod mollusks by 

 measuring with a special instrument the degree of expan- 

 sion or contraction of the pupil produced by the various 

 colors. He found that the yellow and green rays produce 

 much more effect than the red and violet rays. Since this 



