8 COLOR CHANGES IN ANIMALS 



pieces of work led Redfield in 191 S to investigate the 

 effects of this hormone on the chromatophores of the 

 lizard Phrynosoma with the result that adrenalin was 

 found also in this instance to be a potent agent in con- 

 centrating chromatophoral pigment. Redfield, after an 

 exhaustive study of the color changes in Phrynosoma, 

 expressed the opinion that the melanophores in this 

 lizard were under the control of two types of agents, 

 nervous and hormonal, and that both these agents in 

 this particular instance were concerned with the concen- 

 tration of the melanophore pigment, that is, with the 

 blanching of the animal. Here then was evidence of a 

 novel form of chromatophoral control, one in which hor- 

 mones or, as these particular hormones are now called, 

 neurohumors, are concerned. 



In amphibians and crustaceans the process of nerve 

 cutting as carried out by the older investigators had 

 never yielded, even in the hands of the most skilful, 

 conclusive and satisfactory results such as had been ob- 

 tained from fishes and reptiles. It is therefore not sur- 

 prising that skeptical investigators of this subject should 

 turn their attention to amphibians and crustaceans with 

 the view of ascertaining what can be learned from them 

 as to the control of chromatophores. As Hogben (1924) 

 remarks in his volume on the Pigmentary Effector Sys- 

 tem, this line of attack was especially suggested by the 

 researches of Adler (1914), P. E. Smith (1916), and Allen 

 (191 7), who developed the technique of hypophysec- 

 tomy in anuran larvae and called attention to the ex- 

 treme pallor which comes over these young animals after 

 the removal of the germs of their pituitary glands. 

 These workers, however, did not appreciate clearly the 

 full significance of such pigmentary changes; this was 

 first pointed out by Atwell (191 9). In 1921 Swingle 

 noticed that tadpoles darkened when the intermediate 



