BEHAVIOR OF VERTEBRATES 449 



depend upon the preponderance of this or that sense in the 

 life of the species. If the eye plays the chief role in the life of 

 the species it is light which regulates the relations of rest and 

 activity; if other senses have the preponderance, smell, hearing, 

 kinaesthesis, these are the factors which lead to a different 

 division." 



Amphibians. — Laurens (19) investigated the reactions of nor- 

 mal and eyeless amphibian larvae to light. The forms which 

 he used were Rana pipiens, R. sylvatica and Ambly stoma punc- 

 tatus. Neither normal nor blinded frog tadpoles gave any re- 

 sponse to light stimulation. The behavior of Amblystoma, 

 however, was different. Both normal and blinded individuals 

 were found to be positively phototropic. These reactions, as 

 proved by operative surgery, were not due to direct stimulation 

 of the central nervous system but by stimulation of nerve ter- 

 minals in the skin. 



Fish.^*-M.ore work on the color adaptations of fish has been 

 done by Freytag (6). He used Phoxinus laevis, von Frisch's 

 best subject, and tried it over many backgrounds. His exper- 

 iments lasted a year and he used in all 100 animals. These 

 animals were described minutely before and after the experiments 

 and sometimes they were kept for 24 hours on the same back- 

 ground. There were always control animals. As a result of 

 this work Freytag thinks that the adaptations are to brightness 

 and not to color at all. There is no doubt he says that the 

 brightness affects the animals, but no law can be formulated. 

 Not infrequently was there no change and quite as frequently 

 was the change in the opposite direction from what was to be 

 expected. The yellow and red markings showed very incon- 

 stant changes and never was yellow or red the rule. On the 

 other hand these colors were often seen when the fish were over 

 other colors or over gray. He thinks the changes which do 

 occur are not a response to background alone but are due to 

 other conditions as well. The enemies of the fish do not all 

 come from above. It is quite as possible that the adaptation 

 may be to the brightness of the water in which it swims. None 

 of the work speaks for a color sense for Pfrille. 



Two other investigators (9) in the main confirm the findings 

 of von Frisch. 



