BEHAVIOR OF VERTEBRATES 423 



The Purkinje effect is absent in the totally color-blind, and if 

 the fish are totally color-blind as Hess maintains, one could not 

 explain a true Purkinje effect. 



Reptiles and Amphibians. Experiments by Casteel (5) on the 

 turtle {Chrysemys marginata) bring out the fact that the animals 

 failed to discriminate between patterns. Four animals learned 

 to discriminate between black and white, while one failed to 

 show improvement in 220 trials. Two learned to discriminate 

 vertical and horizontal lines and two between two series of 

 parallel horizontal lines 8 mm. and 2 mm. in width respectively. 

 One turtle learned to discriminate between two series of parallel 

 vertical lines 8 mm. and 1 mm. wide and then between lines 4 

 mm. and 2 mm. wide and finally between lines 3 mm. and 2 

 mm. wide. Although not carefully tested, the retention of 

 such habits was surprisingly good. 



Casteel states that the turtle does not learn rapidly. One 

 hundred and eighty-three trials were the average necessary to 

 complete the above habits. From extended experiments (Hop- 

 kins) in which monkeys, dogs, rabbits and rats have been used 

 as subjects in discrimination experiments it would appear that 

 the turtle learns rather rapidly. It is not at all unusual for the 

 above animals to require 200-600 trials to perfect similar dis- 

 criminations. 



Victor Bauer (2) defends the view that the visual purple 

 functions in daylight vision as well as in twilight vision. His 

 experiments were carried out upon frogs and rabbits. The 

 retinae of these animals were exposed to light for varying periods 

 under varying conditions, and the color of the retina was then 

 determined. From his results he finds support for the following 

 general conclusions. When the visual purple is bleached by 

 the action of light, certain products are split off. Some of these 

 products enter into reaction with the nerve substances and 

 stimulate them, while others act upon the secretory epithelium 

 surrounding the retina. The secretions resulting repair or 

 reconstruct the bleached-out purple. The waste and repair of 

 the visual purple takes place not only in dim twilight but even 

 in strong daylight. This may be shown in the isolated bulb, 

 in which the " Restitutionskraft " of the secretory epithelium is 

 gradually exhausted by removal from the body. If sudden 

 strong illumination is admitted to the eye which has been pre- 



