REACTIONS OF MELANOPHORES 197 



Pernitzsch ('13) also found that when Axolotl larvae were 

 kept in darkness they became dark, due to the expansion of 

 the melanophores. 



The results which were obtained from the study of the reac- 

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

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

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

 the assumption that both phases of the movement of the melan- 

 ophores are normally, by means of the eyes, under the control 

 of the nervous system, although it seemed necessary to regard 

 one of the influences of the retinae as inhibitory and opposite 

 in effect to that which causes the pigment cells to contract. 



It was found that the melanophores of normal and eyeless 

 larvae of A. punctatum and of A. opacum react in identically 

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

 the only difference being that the reactions came about more 

 quickly in the normal than in the eyeless larvae. Later the 

 melanophores of normal larvae were found in the opposite con- 

 ditions, in light and in 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 darkness, the melanophores are expanded. The 

 melanophores of eyeless larvae did not show these secondary 

 reactions. 



EXPERIMENTAL 



The same methods employed in my former work on the pig- 

 mentation of Amblystoma larvae were carried out here. The 

 optic vesicles of the eyeless individuals were removed at the 

 tail bud stage (Laurens '14, p. 197), and the eyeless and nor- 

 mal larvae were kept in individual dishes. The melanophores 

 were observed under the binocular microscope, attention having 

 been already called to the inaccuracy of the method of simply 

 observing the general coloration of the animals as an index of 

 the contracted or expanded condition of the pigment cells. 



As in the case of A. punctatum only the subepidermal or corial 

 melanophores are referred to in the following description. The 



