MULTICELLULAR ANIMALS AND COLOR 343 



these organisms, contrary to the hypothesis of Loeb and 

 Davenport, are most strongly affected by the green and 

 yellow rays; (2) that this effect is dependent primarily 

 upon the length of the waves and secondarily upon the 

 amplitude or energy; (3) that these organisms can be 

 stimulated by the ultra-violet and by all the rays in the 

 visible spectrum, except perhaps those near the infra-red; 

 (4) that the stimulating efficiency is not proportional to 

 the energy contents; and (5) that the distribution in the 

 spectrum of stimulating efficiency in these organisms dif- 

 fers from that in a majority of the lower forms, in which 

 it has been clearly demonstrated that the blue or violet 

 rays are the most active. This indicates that the chemical 

 changes associated with the reactions are not the same in 

 all organisms. 



5. Experiments of Graher on Various Animals 



The experiments of Graber on the reactions of animals 

 to colored light are the most extensive of any yet made in 

 this line. He tested 54 different species, — 5 mammals, 

 7 birds, 2 reptiles, 3 amphibia, 2 fishes, 3 moUusks, 27 

 insects, 2 spiders, and 3 worms. Nearly all of these 

 species have well-developed eyes. Besides these in the 

 normal state a blinded amphibia and a blinded insect were 

 tested. 



Following the work of Bert and Lubbock, Graber at- 

 tacked the problem from the psychological point of view. 

 The foremost question with him appears to have been: 

 Do the animals perceive color? In nearly all the experi- 

 ments he studied the change of distribution of the animals 

 in suitable boxes or troughs, the two halves of which were 

 illuminated with light of different colors or different inten- 

 sities, and recorded the number which collected in each 

 half of the inclosure. He does not state how the animals 

 reacted so as to aggregate in one or the other of the light 

 conditions. The aggregations may have been due to 



