ADAPTIVE CHANGES IN COLOR OF FUXDULUS. 69 



showing that the guanophores have the same optical property as 

 was present in the integument. 



B. Shade Adapted to White, Gray, and Black Backgrounds. 



As is well known for many species, changes in shade are due to 

 contraction or expansion of the melanophores. Ballowitz (1893) 

 has shown that the chromatophores of fishes are innervated by 

 branches which proceed from a dense nerve-net surrounding the 

 chromatophores, or even direct from a nerve bundle itself. These 

 con>titute the true pigmento-motor nerves. According to Ballo- 

 witx, they have many free terminations on and within the chro- 

 matophores. As already pointed out, the eye acts as the receptor 

 and the stimulus is conveyed by way of the sympathetic nervous 

 system to in lor fibers innervating the chromatophores as Pouchet 

 -urmi/ed and von Frisch clearly demonstrated. Von Frisch 

 maintains that a centre for contraction of the melanophores 

 exists at the anterior end of the medulla. 



On a white background the melanophores and xanthophores are 

 u-'l. On a black background the melanophores are ex- 

 led and the xanthophores are contracted. In the male -speci- 

 men- tin- - I very bars and the bright mottled condition of the 

 lateral i",ni"iis are retained no matter how long the fishes are left 

 in thi> i-minniment. In fact, they are more pronounced by con- 

 with the dark ground-color of the fish. No evidence of a 

 reduction or increase in the number of melanophores after a pro- 

 l"ii. iinilus in the white or black environment was observed, 



such as Kuntz (1917) asserts to be the case in Paralichthys. On 

 ray background the specimens were intermediate in shade, the 

 nielanophores being partially contracted. 



C. Yellow Adapted. 



The melanophores in specimens exposed to a yellow background 

 i"<ii :1 weeks were maximally contracted. The xanthophores 



on the other hand were maximally expanded, to such an extent 

 that they appeared diffused and the limits of the individually pig- 

 ment cells were difficult to determine. In this condition, the 

 blue retlecting layer is largely concealed. Examined by a reflected 

 light, the brilliant points on the scattered melanophores are very 

 striking, the predominant colors reflected being yellow and orange. 



