148 JOHN N. LOWE 



majority of the physiological researches upon the melanophores, 

 the experiments have only included the study of such physical 

 agents as light, heat, etc. The problem here undertaken was to 

 determine the reactions of the melanophores of young trout em- 

 bryos in response to changes in their chemical environment. The 

 trout embryos that were used in these experiments were too 

 young to react to a change in the light conditions, and through- 

 out the work gave no evidence of any psychic influence of the 

 pigment cells. 



MATERIAL AND METHODS 



Young brook trout embryos, from two days to two weeks after 

 hatching, were used. The melanophore of such young individuals 

 are dark, much branched cells with deep black or brown pigment 

 granules. These are the only kind of pigment cells present at 

 this time. The xanthophores, the yellow or reddish pigment 

 cells, appear after or a little before the yolk is absorbed. All the 

 experiments were performed before the xanthophores appeared. 

 After the yolk is absorbed the fish begin to react to the back 

 ground. When placed in a dark dish, they become dark; when 

 placed in a white dish, light in color. Microscopical examina- 

 tion shows that the pigment cells (melanophores) are expanded 

 in the dark colored individuals and contracted in the light ones. 

 The very young, two-day or two-week old embryos do not 

 respond to changes of the back ground. 



This constant condition is taken as a known factor. The 

 contraction of the pigment cells was used as the criterion for 

 determining stimulation, and their expansion (relaxation) as a 

 mark of depression. The expansion of the pigment cells is char- 

 acterized by the peripheral migration of the pigment granules 

 within the processes of cell, and in contraction the movement is 

 centripetal. My reason for considering contraction as stimula- 

 tion and expansion as a depression is that certain reagents, alka- 

 loids for example, if used in high concentrations produce no ob- 

 servable change in the pigment cells which under normal con- 

 ditions are expanded. Small or 'therapeutic' doses produced a 



