REACTIONS OF MELANOPHORES OF AMBLYSTOMA 241 



The stimulation of the retinae (illumination) produces a con- 

 traction of the melanophores, and as the eyes continue to develop 

 and finally gain the upper hand in the sense life of the animal, 

 so the impulses started by illumination of the retinae become 

 stronger and finally overcome entirely the inhibitory influence 

 of the parietal organ, so that in light the melanophores are con- 

 tracted. Now, if the influence of the eyes is removed, by blind- 

 ing the larvae, then the parietal organ is again in complete con- 

 trol, and the melanophores therefore expand in the light. 



The remainder of this theory of Fuchs is as interesting as what 

 has gone before. He goes on to say, that whether all larvae 

 have a functional parietal organ, and whether the functioning 

 power decreases as the development of the animal proceeds — ■ 

 which he considers probable — can be learned only experimentally. 

 If this is found to be true then, he believes, it will be easy to 

 understand why in adult animals the eyes have no particular 

 influence over the color changes. For when the eyes have over- 

 come the opposite influence of the parietal organ then after the 

 extinction of its influence the function of the eyes must naturally 

 in this respect also be less, because their antagonist, the stimu- 

 lation of which causes the pigment cells to expand, is lacking. 

 In other words, Fuchs would claim that the pigment motor func- 

 tion of the eyes, by means of which contraction of the pigment 

 cells is brought about, is developed to offset an opposite effect 

 of the parietal organ, and after this has been overcome it dis- 

 appears. Moreover in his theory, nothing is said concerning 

 the direct stimulation of the pigment cells by light, and no indi- 

 cation is given as to just how the chromatophores are stimulated 

 after the influence of the eyes as well as that of the parietal 

 organ has been extinguished. 



EXPERIMENTAL 



The work, the results of which will be given in the succeeding 

 pages, was undertaken to put to experimental test this theory 

 of Fuchs. More particularly to see whether the parietal organ 

 in young normal seeing larvae can be shown to exert any in- 

 hibiting influence upon the melanophores, which later disappears 



