134 The Animal Mind 



periment was repeatedly performed, and the greatest num- 

 ber was always found in the yellow-green region (249, 250). 

 Bert obtained similar results with the use of an electric light 

 spectrum; but besides throwing all the colors at once upon 

 the vessel, he allowed each color to act separately through a 

 narrow opening, and noted the speed of the positive response 

 produced. That the "preference" shown for yellow- green 

 light is not a matter of color vision, but of response to the 

 greater intensity of the light in this region of the spectrum, 

 was suggested by Bert (24), and Merejkowsky showed that 



the larvae of Balanus 

 and Dias longiremis 

 manifested no color 

 preference when the 

 colors were made of 

 equal intensity (269). 

 Lubbock attempted 



FIG. ii. Daphnia. at, antenna; atl, antennule; to prove the exist- 

 OC ,eye. After Yerkes. ence Q f qua li t ative 



as distinguished from intensive discrimination by various 

 modifications of the experiment, but without entirely con- 

 clusive results (251, pp. 221 fL). Finally, Yerkes, working 

 on Simocephalus, a form closely related to Daphnia, found 

 that when a gaslight spectrum was used, the animals col- 

 lected in the red-yellow region, that of greatest intensity for 

 such light ; and that if this region had its intensity diminished 

 by a screen of India ink or paraffin paper, the crustacean 

 moved out of it (448). In all probability, then, the reactions 

 of these forms are not accompanied by qualitatively different 

 color sensations corresponding to light of different wave 

 lengths. 



That Daphnia seeks a region affected by the ultra-violet 

 rays of the spectrum in preference to darkness, although the 



