Sensory Discrimination : Vision 129 



will cause them to reach up and sway from side to side in 

 apparent search for prey (438). 



A curious effect of colors on tube-dwelling worms has been 

 observed. When placed under either blue or red glass, the 

 sensory activities of the worms seemed to be inhibited for 

 a time, the effect being more striking in the case of the red 

 glass. When brought suddenly from under blue glass into 

 ordinary white light, the worms showed intensified reactions ; 

 while bringing them from under red glass to white light in- 

 hibited their reactions for from two to five minutes (158). 



The fact that animals which display positive phototropism 

 show also an "aversion" to red and a tendency to seek colors 

 that contain the ultra-violet rays, while negatively phototropic 

 animals avoid light that has ultra-violet rays, and seek red, 

 which lacks these rays, has pointed to the probability that 

 apparent color discriminations in the lower forms of animals 

 are really reactions to the intensity of the light, and espe- 

 cially to the intensity of the ultra-violet rays. This position, 

 however, has recently been questioned by Minkiewicz. He 

 has succeeded in changing the reactions of a Nemertean 

 worm, Linens ruber, to colored light, while its response to 

 white light remained unaltered. 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's chromotropism was again inverted, 

 becoming positive to the violet rays, while negative phototrop- 

 ism persisted. Moreover, intermediate stages in the passage 

 from the red- to the violet-seeking phase were observed; a 

 stage where, still positive to red, the animal ceases to distin- 

 guish red from yellow, and others where it seeks violet, but has 



