316 ALFRED C. REDFIELD 



fluctuations in the state of the pigment cells which make up the 

 daily rhythm are to be explained. 



Figure H is a, schematic representation of the various factors 

 which influence the tone of the melanophores of the horned toad. 



3. Comparative physiology of the melanophores of vertebrates 



a. The influence of hormones upon melanophores. Since many 

 of the more extensive investigations of melanophores were made 

 before the study of the endocrine glands assumed the important 

 place in physiology which it holds to-day, it is not surprising that 

 only one attempt has heretofore been made to associate melano- 

 phore reactions with hormones. The suggestion of Fuchs, ('14), 

 that a secretion of the pineal organ may influence melanophore 

 reactions, has been shown on page 295 to be unsupported by the 

 known facts. The only other studies which bear upon the present 

 point are a number of isolated observations that adrenin causes a 

 contraction of melanophore pigment. This observation has been 

 made upon the frog by Corona e Moroni ('98) and by Lieben ('06), 

 and upon Fundulus by Stockard ('15) and by Spaeth ('16a). 

 These authors do not suggest, however, that activity of the 

 adrenal glands is correlated with the condition of the melano- 

 phores in nature. 



In some unpublished experiments upon Anolis carolinensis, 

 it was found that the melanophore pigment is contracted during 

 nervous excitement, that this contraction could be blocked 

 momentarily in one leg by tying a ligature about it, and that 

 injection of adrenin produced the green color of the skin. It 

 would not be surprising if a more extensive study should show 

 that the conditions found in the horned toad also exist in this 

 lizard.^ 



* Since this paper was written an article has appeared by Ruth and Gibson 

 ('17) in which it is stated that the skin of several species of Philippine house liz- 

 ards becomes blanched through the action of adrenin and mechanical irritation. 

 They consider their results similar to those described in an earlier paper (Red- 

 field 1916) . These authors take the novel view that this color change is due to 

 a bleaching of the pigment rather than to a change in the position of the mel- 

 anin granules in the skin. 



