BEHAVIOR OF VERTEBRATES 419 



of the other. Yet, he says, fish are known to perceive differences 

 in brightness which are as 1 : 1.23. Hence von Frisch's assump- 

 tion that the color of a fish proves that it recognizes this color 

 as identical with that of its background is unproven. Hess 

 believes that color adaptation may be due to brightness or to 

 the intensity values of light or it may not have a visual cause 

 at all and he cites Dorflein's experiments with crabs which were 

 kept in the dark and yet turned red. Crenilabri were also used 

 by Hess. Part of the fish were put in a ruby glass aquarium 

 with a background of white walls and the others in a black aqua- 

 rium covered with a black cloth. After eight days it is said, no 

 observer could see any difference in the fish. Fish were trained 

 by him for yellow food but could not distinguish it against a 

 blue ground or a gray of the same brightness. He thinks Wash- 

 burn and Bentley could draw no conclusions from their work 

 on the color vision of fish because of their method. 



He insists that a protective device to be effective must take 

 place in a few minutes and not in a few hours. The facts of 

 color adaptation in the human retina are alleged as against the 

 assumption. 



In answer to the evidence of the Hochzeitkleid for vision he 

 declares that fish which spawn at a depth of from six to eight 

 meters cannot see red. Red can be seen directly at from three 

 to four meters but viewed obliquely it is brownish or grayish. 

 Markings, therefore, can be of little value in deep water and 

 yet fishes which spawn at great depths have these markings. 

 In all his work Hess clings to the belief that fish have the vision 

 of color-blind men. 



Von Frisch in reply to this last argument gives a long list 

 of fish with the depths at which they spawn and the time of 

 spawning, i.e., night or day. He admits that many of the fish 

 which spawn at night have brilliant colors. But, he says, when 

 it is seen that most varieties take on color at spawning time, and 

 at no other time, and that it is always characteristic of those 

 which spawn in shallows, where conditions are favorable for the 

 perception of brilliant color, it is only natural to believe that 

 the wedding dress is an attractive cloak. 



Birds. Bingham (4) investigated the perception of size and 

 form in chickens, using the Yerkes-Watson apparatus, which 

 is described in the Behavior Monograph (1911, vol. 1, no. 2). 



