462 PROCEEDINGS OP THE AMERICAN ACADEMY. 



The effects of heat on the change from green to brown has also been 

 worked out, as in the case of the opposite change, and the results are 

 given in Table II. 



At 10° the animals became brown, and, as in the former records at this 

 temperature, they remained so, irrespective of illumination. Their rate 

 of change at this temperature could not therefore easily be determined. 

 Green animals, however, when introduced into the dark, constant- 

 temperature box changed to brown in about 18 minutes, but this record, 

 which was obtained only after opening the box and handling the animals, 

 can be regarded as only approximate. Its slowness is doubtless due to 

 the circumstance that it represents a conflict between two opposing con- 

 ditions : dark, inducing the green state, and low temperature, inducing 

 the brown one ; for when green lizards were introduced into the lighted 

 box at 10° they changed to brown in 2.55 minutes. 



From 20° to 35° the green animals when in the dark remained green, 

 a condition determined not by temperature but by the absence of light, 

 for when they were exposed to light at these temperatures they changed 

 to brown at ever-increasing rates from 4.23 seconds at 20° to 2.80 

 seconds at 35°. Although heat between 20° and 35° is no more the 

 controlling factor in the change from green to brown than it is in the 

 reverse change (Table I), its influence is seen in the increased rate of 

 the change, characteristic of the range from 20° to 35° under uniform 

 illumination. 



At 40° and 45° green animals, as might have been expected, remained 

 green or greenish gray, irrespective of the illumination. 



From these two sets of records it is evident that at a low temperature 

 (10°) the lizards change from green to brown but not the reverse, and 

 remain brown irrespective of illumination (115 candle-metres). At high 

 temperatures (40° and 45°) they turn from brown to green but not the 

 reverse, and remain green or greenish irrespective of illumination (115 

 candle-metres). Between these two extremes, at both of which heat is 

 the controlling factor, there is a range (20° to 35°) through which light 

 is the controlling factor, though heat here is not without its influence. 

 This is indicated by the differences of rate in the changes from brown 

 to green (Table I) and green to brown (Table II), accompanying the 

 differences of temperature. 



Thus it is well established that the rate of the color changes in Anolis 

 is always more or less influenced by temperature, and the discrepancies 

 between our early results and those of Carlton undoubtedly depended 

 chiefly upon this factor, for Carlton's experiments were carried on in a 



