MELANOPHORES OF THE HORNED TOAD 281 



inner jar could be kept within a degree or two of a given tem- 

 perature. In the inner j ar was placed a layer of sand, which served 

 to keep it floating upright and gave a natural support for the 

 animal. This jar was kept covered to maintain the temperature 

 and humidity as constant as possible. When desired light was 

 excluded from this apparatus by inverting over it a large paste- 

 board box. 



November 26, 1913. Two horned toads, the melaiiophoie pigment of 

 which was expanded, were placed in the apparatus at 10.45 A.M. 

 They were illuminated by the light from the overcast sky. Warm 

 water was placed ih the outer jar. 



After one hour (11.45 A.]M.) the temperature of the air in the inner 

 jar had risen to 40°C. and the melanophore pigment of the animals had 

 contracted. 



One-half hour later (12.15 P.M.), the temperature of the air in the 

 inner jar had fallen to 26°C. and the melanophore pigment had ex- 

 panded slightly. Ice was added to the water. 



Nearly two hours later (2.00 P.M.), the temperature was found to be 

 16°C. and the pigment was fully expanded. The apparatus was then 

 covered with a box to exclude the light. 



After one-half hour (2.30 P.M.) the melanophore pigment was still 

 expanded. Temperature 17°C. The ice-water was replaced with 

 warmer water. 



One hour later (3.40 P.M.) the temperature had risen to 25°C. and 

 the pigment had contracted again. It remained in this condition as the 

 temperature was raised to 36°C. at 4.20 P.M. 



Repeated experiments confirm the conclusions which may be 

 drawn from these data. It makes no difference in which order 

 the changes of temperature and illumination are arranged. 



The following summary indicates the condition of the melano- 

 phore pigment under various conditions of temperature and 

 illumination : 



1. High temperatures produce a contraction of the melano- 

 phore pigment, irrespective of illumination. 



2. Low temperatures produce an expansion of the melanophore 

 pigment, irrespective of illumination. 



3. At intermediate temperatures (30° to 20°C.) the state of the 

 melanophores is conditioned by the illumination, light causing 

 an expansion and darkness a contraction of the pigment. 



