away from the light, was of the brightest tint. The same relationship between 

 the illuminated and the unilluminated side was seen on many occasions. 



This appears to be a most interesting adaptation — a dynamic manifestation 

 — of the principle discovered in its static form by Mr. Abbott H. Thayer. Mr. 

 Thayer first suggested that the relative shades of the dark back, lighter sides, 

 and white under sides of animals were such as just to counterbalance the 

 diminution of natural illumination from an open sky as we pass from the 

 back down the sides to the under surface; that the object of this counter- 

 grading was to neutralise the shadow which would otherwise render the 

 animal conspicuous. C. pumilus, as I have said, manifests the same principle 

 in a dynamic form. The side that happens to be turned away from the 

 light is brightened sufficiently to neutralise the shadow; the high illumination 

 of the other side is toned down by darkening, the effect being that all appear- 

 ance of solidity is dissipated. This result must be of great importance to so 

 large and so defenceless an animal as the chamseleon. But for this adjustable 

 countergrading, the varying degrees of illumination on the side and dorsal 

 slope turned towards the light, combined with the strong shadow on the other 

 side, would cause it to stand out among the leaves as an object of conspicuous 

 sohdity and thickness. 



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