2 COLOR CHANGES IN ANIMALS 



of Avon play his part in transmitting truth and fancy 

 about this interesting creature. It must be clear from 

 these few allusions that the subject of this lecture has 

 both the venerableness of age and the dignity of poetic 

 association. 



From very early times till about the beginning of the 

 present century color changes in animals were believed 

 by the majority of workers to be under the exclusive 

 control of the nervous system. This opinion, often only 

 vaguely and generally expressed, steadily gained ground 

 in consequence of the accumulation of a large body of 

 favorable evidence drawn in part from purely observa- 

 tional work and in part from experimental investiga- 

 tions. One outcome of these inquiries was to show that 

 the eyes of animals are essential to their color changes, 

 for when these organs were removed or effectually cov- 

 ered all signs of such changes disappeared, and the given 

 animal so far as an alteration of its tint was concerned 

 was largely incapacitated. In normal animals the color 

 changes had long been recognized as means of harmon- 

 izing the creature with its surroundings. Even Aris- 

 totle in describing the habits of the common octopus 

 remarked that this cephalopod would pursue any fish 

 that came in its way, changing its color so as to imitate 

 that of the neighboring rocks. This it also did when 

 alarmed. In 1830 Stark, who had studied the color 

 changes in a number of British river-fishes such as the 

 perch, minnow, and the like, observed that when these 

 fishes were on a light background they were pale in tone 

 and when they were on a dark one they were of a deeper 

 shade. He advanced the idea that this agreement, by 

 which the fish was lost, so to speak, in its own back- 

 ground, was an advantage to it in its escape from ene- 

 mies. This and other instances of a like kind gave rise 

 to the modern theory of protective coloration, a system 



