16 Lvolution 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 
