MELANOPHORES OF THE HORNED TOAD 309 



Etherized the animals and removed the adrenal glands. 



August 12, 1916. Melanophore pigment was uniformly expanded. 

 Stimulated mouth as before for ten minures. The back anterior to the 

 point of transection of the spinal cord, the fore limbs and all the lateral 

 scales became very distinctly paler. The melanophore pigment of poste- 

 rior part of the body remained fully expanded. 



This experiment demonstrates clearly the mechanisms con- 

 cerned in the coordination of the melanophores. Before removing 

 the adrenal glands the melanophore pigment of a portion of the 

 skin which is isolated from the nervous system may be made to 

 contract ; after removing these glands this reaction can no longer 

 be brought about. It is thus unquestionably proved that the 

 secretion of the adrenal glands is one factor in the coordination of 

 the melanophores. 



After the adrenal glands have been removed it may also be 

 clearly seen that the nervous system is directly concerned in the 

 coordination of melanophores. It is then possible to cause a 

 contraction of the melanophore pigment of the entire skin, 

 excepting those parts which have been isolated from the rest by 

 the transection of nerves. 



It now^ becomes quite clear why cutting nerves to a part of the 

 skin does not prevent the melanophore pigment of that part from 

 contracting when the animal becomes excited, and why removing 

 the adrenal glands usually does not block this reaction com- 

 pletely. The melanophores are coordinated by two distinct mechan- 

 isms, the adrenal secretion and the direct action of nerves. Either 

 mechanism alone is capable of causing the melanophore pigment to 

 contract. It is consequently necessary to isolate the melanophores 

 from both factors before their reactions are blocked, 



A fe\V horned toads have been found in which removal of the 

 adrenal glands alone has served to block the reaction of the 

 melanophores to noxious stimuli. In other individuals stimula- 

 tion of the sciatic nerve has failed to cause the melanophore pig- 

 ment of the leg to contract. These facts suggest that in these 

 individuals the nervous control of the pigment cells was not fully 

 developed. In animals from which the adrenal glands have been 

 removed the contraction of the melanophore pigment is never as 

 great as that produced by the combined action of the adrenal 



