ANIMAL TINCTUMUTANTS. 391 



found in the cutis of the embryonic chick, about the fifteenth day, 

 certain pigment cells. These cells have entirely disappeared by 

 the twenty-third day. It is probable that little, if any, light can 

 reach the chick through the shell and membranes, yet pigment 

 cells develop and disappear again. 



A butterfly emerges from the cocoon arrayed in all the colors 

 of the rainbow, yet it was developed, while in the -pwpa state, in 

 total darkness. It is not necessary to mention further instances ; 

 we readily see that pigmentation in animals is not necessarily de- 

 pendent on light. Neither is tinctumutation the result of the 

 direct influence of light on the chromatophores. Light, however, 

 if not the direct, is the indirect cause of this phenomenon. Lister, 

 in 1858, showed that animals with imperfect eyesight were not 

 good tinctumutants, notwithstanding the fact that they had the 

 chromatic function. He showed, by his experiments on frogs, 

 that the activity of the chromatophores depended entirely on the 

 healthy condition of the eyes that is, so far as the phenomenon 

 of tinctumutation was concerned. So long as the eyes remained 

 intact and connected with the brain by the optic nerve, the light 

 reflected from surrounding objects exerted a powerful influence 

 on the chromatophores. As soon as the optic nerve was severed, 

 the chromatophores ceased to respond to the influence of light 

 and color, no matter how bright and varied they were. The de- 

 ductions drawn from these experiments are not to be controverted 

 or denied. The chromatophores are influenced by light reflected 

 from objects and transmitted via the optic nerve to the brain ; 

 from this organ the impression or irritation goes to the nerves 

 governing the contractile fibers of these pigment-holding glands. 



Pouchet followed Lister and confirmed his conclusions by ex- 

 periments on fishes and crabs. He remarked that the plaice, a 

 fish with a white under surface and a particolored back, had the 

 chromatic function highly developed. Among a number of speci- 

 mens which appeared pale on the white sandy bottom, he met 

 " one single dark-colored fish in which, of course, the chromato- 

 phores must have been in a state of relaxation, and this specimen 

 was as distinct from its companions as from the bottom of the 

 aquarium. Closer investigation proved that the creature was 

 totally blind, and thus incapable of assuming the color of the 

 objects around it, the eyes being unable to act as a medium of 

 communication between them and the chromatophores of the 

 skin." Thus far Pouchet had only confirmed Lister's observa- 

 tions, although it is highly probable that he was unaware of Lis- 

 ter's experiments. But he went a step further. There are two 

 ways in which cerebral impressions may be transmitted from the 

 brain to the skin : one, by way of the spinal cord and the pairs of 

 nerves arising from it and known as spinal nerves. ; the other, by 



