Studies in amphibian colour change.—II

The author, in a previous paper, has dealt with the normal reactions ofRana termporaria to various environmental factors. It is hoped here to deal with the method by which these factors influence the mechanism which, in turn, produces the characteristic responses in the melanophores. The effect of the background has been shown to be as follows :— Light background tends to produce pallor; Dark background tends to produce darkening. Parker has shown that the frog makes heliotropic movements when it is blinded, and postulates that it possesses some receptor organ in the skin sensitive to light. It may be suggested that the frog only perceives the stimulus of heat. At the present state of the investigations it is impossible to distinguish between the two. For the frog shows a definite response to heat stimuli similar to the response to light. Experiments were carried out to show whether the frog would respond to background when blinded. For this purpose it was not necessary to repeat all the combinations of factors employed in the normal reactions. Many of these would not show any difference from the normal as the other factors tend to produce the same result as the background, so that if the factor of background were eliminated by blinding the frog the response would be in the same direction as before and thus not be plainly demonstrable. Those conditions found to be most suitable for these experiments are :— Ex. 1. { Mt+L+Lb+W Ex.2. { Lt+L+Lb+D Mt+L+Db+D Lt+L+Db+D*