712 



Comparative Animal Physiology 



responsive to certain environmental stimuli, changing reversibly through the 

 spectral colors to red on excitation and in the opposite direction on recovery. 

 This response is direct, and does not in\olve coordinating mechanisms within 

 the animal, either nervous or humoral.^" 



Reptiles. The functional organization of the melanophores of reptiles 

 shows, as in the fishes, a great diversity. It appears to involve, to differing 

 degrees in different reptiles, the acti\'ities of hormones and nerves. 



The melanophore responses of the iguanid, Anolis, have been iuACsti- 

 gated very extensively by Kleinholz.'''^ These lizards show color changes 

 ranging from bright green to dark brown. They typically assume the former 

 color in an illuminated white container, and the latter in an illuminated 

 black one. The response to change from a white to a black background is 



Fig. 274. A normal dark and a hypophysectomized light Anolis. From Kleinholz."" 



usually completed in 5 to 10 minutes. The reverse change normally re- 

 quires 20 to 30 m.inutes. These background-induced responses depend on 

 the eyes; they cease after bilateral blinding. However, such blinded speci- 

 mens still are capable of color change; they darken in light and become 

 pale in darkness, through primary responses. 



For many years after Briicke's-*'' classical studies of color change in the 

 chameleon, in which he demonstrated nervous control of the melanophores 

 by the sympathetic system, it was considered that reptilian chroma tophores 

 generally were thus controlled. Studies on Phrynosoma,^''^ however, pro- 

 vided basis for a strong suspicion that nerx'es were not the sole method of 

 control. The lizard, Hemidactylus, becomes pale in color after hypophysect- 



