MULTICELLULAR ANIMALS AND COLOR 



341 



iently bright to them, and that they can distinguish be- 

 tween hght of different wave-lengths. I suppose it would 

 be impossible to prove that they actually perceive colors; 

 but to suggest that the rays of various wave-lengths pro- 

 duce on their eyes a different impression from that of 

 color, is to propose an entirely novel hypothesis. 



" At any rate, I think I have shown that they do dis- 

 tinguish between rays of different wave-lengths, and prefer 

 those which to our eyes appear green and yellow." 



The striking positive reaction to yellow and green in 

 preference to white light of a higher intensity seems to 

 indicate that Daphnia is negative to the other rays of the 

 spectrum. This question has been discussed elsewhere. 



4. Experiments of Yerkes on Simocephalus 



Yerkes (1899) made a very thorough study of the re- 

 actions of Simocephalus vetulus, a form similar to Daphnia, 

 both in gas and sunlight spectra. Every reasonable pre- 

 caution was taken in the manipulation of the apparatus. 

 The method employed was like that used by Lubbock on 

 Daphnia. The following table shows the relative numbers 

 which collected in the different regions of the two spectra: 



TABLE XIV. (After Yerkes, 1899.) 



Since Simocephalus is positive even In direct sunlight, it 

 is safe to say that It Is positive to the light conditions of 

 that part of the spectrum In which it aggregates. The 

 table above shows clearly that in the gas spectrum most of 



