BEHAVIOR AND COLOR CHANGES OF TREE FROGS 71 



failed to respond in this manner. Carlton ('03 p. 267), found 

 also that section of the cord in Anolis had little if any effect 

 on its color changes, which agrees in the main with my own 

 results. He argues, however, " Since it seems impossible to 

 explain the conditions without assuming some nerves to be 

 involved, and since the only other nerves present are the sym- 

 pathetic, these observations point to the sympathetic fibres as 

 the ones controlling the change from green to brown." 



It has been a growing conviction with the writer that ex- 

 periments of this character as tests of behavior in particular, 

 and also reactions of many other sorts, are extremely untrust- 

 worthy at best. The very nature of the experiment, — the 

 anesthesia, the operation, and the consequent shock all conspire 

 to involve the organism as a whole in such physiological state 

 as to render reactions more or less abnormal, or even patho- 

 logical. But in any case there must be the greatest care to have 

 results confirmed by the most positive evidence from natural 

 sources. And until we have larger confirmation from such 

 experiments than is at present available prudence will suggest 

 caution in drawing sweeping conclusions. 



Darkness and Light. As shown in the case of H. versicolor, 

 and as noted by other observers, the effect of bright light is 

 often to induce a lightening of the skin color in amphibia. In 

 some cases this takes place rapidly, even in 10 minutes under 

 the strong influence of heat and light. This was found to be 

 more or less true in the case of H. arborea, though the time 

 involved in reaction to light is usually gradual. But it must 

 not be overlooked that exposure to direct sun often involves a 

 higher temperature. In several cases this was found to vary 

 as much as 10 degrees C. within half an hour. From what will 

 be shown in the next section it may appear quite probable 

 that some of the changes one might be disposed to attribute 

 to light are really induced by heat. But even here there are 

 very conflicting results. However, the sum of numerous ex- 

 periments go to deepen the impression that the usual effect of 

 light is to induce a lighter skin color. 



But on the other hand, my experiments of a converse char- 

 acter, viz., touching the effects of darkness, do not show any 

 converse darkening of color. Many experiments were made to 

 test this, and for the most part with negative results. In many 



