1 6 Evolution and Adaptation 



that, while in some cases it may be necessary to replace the 

 lost part if the animal is to remain in existence, as when 

 a new head is formed on an earthworm after the old one 

 was cut off, in other cases the replacement of the lost part 

 appears to be of minor importance, as in the case of the 

 leg of the crab. While we are not, for the moment, con- 

 cerned with the relative importance of the different adapta- 

 tions, this question is one of much importance in other 

 connections and will be considered later. 



The protective coloration of some animals, which is the 

 direct result of a change in color of the animal in response 

 to the surroundings, furnishes us with some most striking 

 cases of adaptive coloration. A change of this sort has 

 been recorded in a number of fishes, more especially in the 

 flounders. The individuals found living on a dark back- 

 ground are darker than those living on a lighter background ; 

 and when the color of the background is changed it has 

 been observed that the color of the fish also changes in the 

 same direction. I have observed a change of this sort from 

 dark to light, or from light to dark, in the common minnow 

 {Fundulus) in accordance with a change of its background, 

 and the same sort of change appears to take place in many 

 other fishes. 



The change from green to brown and from brown to green 

 in certain tree frogs and in the lizard (Anolis), which is 

 popularly supposed to take place according to whether the 

 background is green or brown, is not after all, it appears, 

 connected with the color of the background, but depends on 

 certain other responses of the animals that have not yet been 

 satisfactorily made out. If it be claimed that in summer 

 the animal would generally be warm, and therefore, often 

 green, and that this color would protect it at this time of 

 year when the surroundings are green, and in winter 

 brown, when this color is the prevailing one in temperate 

 regions, then it might appear that the change is of use to 



