REACTIONS OF MELANOPHORES OF AMBLYSTOMA 253 



merits would certainly afford a great deal of evidence con- 

 cerning the influence of the parietal organ on the melanophores. 

 Such experiments should also be carried out on reptiles, where 

 the parietal organ reaches a high degree of development, and 

 in some animal where the color changes of the skin are well 

 marked. 



The nervous system must be admitted to exert a very impor- 

 tant effect upon the chromatophores of any animal, and this effect 

 is for the most part conditioned upon the eyes, which have 

 been shown to play such an important part in the color changes 

 of many animals (see, for example, the reactions which have 

 been described for the melanophores of Amblystoma, or the 

 effects observed by von Frisch, '11 and '12, of blinding fish). 

 Take away the eyes and the major part of the controlling influ- 

 ence of the nervous system over the pigment cells of the skin 

 is lost. This of course does not apply in full to those cases where 

 the eyes have, or are believed to have, lost control over the chro- 

 matophores and where other things than light, such as tempera- 

 ture, tactile stimuli, etc., are believed to be of greater importance. 



But even in such a case, as Biedermann has shown, the re- 

 actions of the melanophores to light are controlled by the nerv- 

 ous system in that this exerts a tonic influence upon the pig- 

 ment cell. Biedermann demonstrated that the pigment cells 

 of the frog as soon as they are released from the influence of the 

 nervous system have the tendency to expand. When he cut 

 through the connection between the thalamus and the mid- 

 brain in Rana esculenta and R. fusca, as well as in Hyla, he found 

 that the melanophores expanded, and that when the frogs (par- 

 ticularly Hyla) operated on in this way are kept for weeks in 

 darkness as well as in diffuse light no change takes place in the 

 melanophores. Briefly, that light has under these conditions 

 little, if any, eflect on the melanophores, unless direct sunlight 

 is used. 



It is my belief that the general function of the chromatophores 

 is to expand when illuminated and to contract again when in 

 darkness. But when the melanophores are under the influence 



