JIEACTIONS OF MELANOPHORES OF . AMBLYSTOMA 239 



impulse for the contraction of the chromatophores originates in 

 the illuminated retinae and is in turn so strong that it overcomes 

 the tendency of the illuminated chromatophores to expand and 

 brings about their contraction. 



The results which were obtained from a study of the reactions 

 of the melanophores of larvae of A. punctatum and of A. opacum 

 (Laurens '15) were such that this explanation of Babak's could 

 not be applied to them. They threw no doubt, however, on the 

 assumption that both phases of the movement of the melano- 

 phores are normally under the control of the nervous system 

 by means of the eyes, although one of the influences of the retinae 

 must be admitted to be inhibitory, and opposite in effect to an 

 impulse which causes the pigment cell to contract. 



The results of my work showed that the melanophores of 

 normal and eyeless larvae react primarily in identically the 

 same way, expanding in light and contracting in darkness, the 

 only difference being that the reactions come about more quickly 

 in the normal than in the eyeless, larvae (p. 585 and table 2). 

 Secondarily, however, the melanophores of the normal larvae 

 are found to be in the opposite conditions in both light and 

 darkness to what they were in before, for after having been 

 kept for from three to five days in light the melanophores are 

 contracted, and after having been for five days or more in dark- 

 ness, the melanophores are expanded. The melanophores of 

 the eyeless larvae do not show these secondary reactions. 



It was assumed (pp. 624-625), to explain these secondary 

 reactions of the melanophores of normal seeing larvae, that, 

 although the primary effects of indirect stimulation of the 

 melanophores through the eyes were the same as those of direct 

 stimulation, in the case of light the constant illumination or 

 stimulation of the retinae had the result of causing impulses to 

 be started, the end effects of which were opposite to those of 

 direct stimulation and in this way the secondary contraction of 

 the melanophores was brought about. These impulses were 

 supposed to have their immediate cause in certain photo-chemical 

 changes taking place in the retinae. In the case of darkness 

 the same thing was supposed to take place, in that, due to the 



