1 68 CHARLES G. ROGERS. 



may indeed be obscured by the action on a change in tempera- 

 ture. If the animals were placed in the dark for several hours 

 they all became darker, if in the light for a number of hours they 

 all became lighter. It was further found that the change in 

 color due to a change in light conditions might be inhibited by 

 contrary changes in the temperature conditions. The following 

 table represents various combinations of light and temperature 

 conditions which have been tested and the results obtained in the 

 coloration of the animals. 



TEMPERATURE. IN DARK. IN LIGHT. 



High, Ordinary, Very Light. 



Low, Very Dark, Ordinary. 



By high temperatures are meant temperatures of from thirty- 

 five to forty degrees Celsius ; by low, temperatures below ten 

 degrees Celsius. 



From the table it is readily seen that we are here dealing with 

 two sets of forces which tend to neutralize each other when 

 applied in opposite directions and to augment each other when 

 applied in the same direction. 



The manner in which this change is brought about is the same 

 as that described by Carlton for Anolis. Small granules of pig- 

 ment migrate outward from the large pigment cells along the ray- 

 like processes of the cells when the animal is placed in the dark, 

 thus obscuring the yellow pigment which lies in the deeper 

 layers of the skin. When the animal is brought again into the 

 light the pigment granules again migrate into the bodies of the 

 pigment cells, and the lighter yellow pigment of the deeper layers 

 of the skin becomes visible. The operation is a rather slow one 

 and may occupy an hour or more of time. 



In certain animals a condition of permanent darkness was 

 established through a section of the optic nerves. So long as 

 the animal had one or both eyes functional the action of the skin 

 was as stated above. When both eyes are made functionless a 

 marked change takes place. Within a short time the skin begins 

 to darken and within two hours has taken on a dark brown, dark 

 green or black color. The appearance of the animals is similar 

 to that produced by the action of darkness and low temperature. 

 At ordinary room temperatures this change is permanent. 



