REACTIONS OF MELANOPHORES OF AMBLYSTOMA 249 



ments in which a narrow beam of light, reflected from a Nernst 

 glower by a mirror and concentrated with a lens, was thrown 

 on the region of the brain from which the epiphysis arises. The 

 results of these experiments give additional evidence concern- 

 ing the ability of the melanophores to respond to direct stimula- 

 tion by light. 



When Amblystoma larvae are placed in darkness and observed 

 by means of a faint red light, they remain motionless for the 

 greater part of the time if there are no other larvae present or 

 other animals which may serve as possible food. It is therefore 

 a simple matter to throw such a beam of light upon any por- 

 tion of the dorsal or lateral surface of the body and keep it there. 

 Naturally, at times the larvae move by alternately crawling 

 and swimming with the snout close to the bottom of the vessel 

 in the characteristic nosing fashion, nevertheless, the animals 

 can usually be followed with the narrow beam of light until they 

 again come to rest. 



It was found that in no case when the beam of light was thrown 

 upon the region of the epiphysis of normal seeing or eyeless 

 larvae did an expansion of the melanophores over the whole body 

 take place. On the other hand the result of such local illumina- 

 tion at any place on the body results in an expansion of the 

 melanophores stimulated. These experiments are rather tedious 

 because of the time consumed in carrying them out. In table 

 2 (Laurens, '15, p. 585) it will be seen that it takes from 1^ to 

 2 hours for the melanophores of normal larvae with eyes to ex- 

 pand when the larvae are placed in the light, and 2 to 3 hours 

 for the same thing to happen in eyeless larvae. In these experi- 

 ments with local illumination no expansion was observed tak- 

 ing place in less than 2 hours and in most cases an illumination 

 lasting 3 hours or more was necessary. 



These experiments on local illumination were carried out on 

 both normal and eyeless larvae with and without the epiphysis 

 and the roof of the diencephalon. In some of them not only was 

 the beam of light thrown on the region of the head under which 

 the epiphysis is, but the brain was exposed and directly illumi- 

 nated. In addition it was also carried out on larvae in which 



