408 EVOLUTION AND ANIMAL LIFE 



others with sand. The toad bug (Galgulus) lives abundantly 

 on the banks of this pond. Specimens collected from the 

 blue rocks are bluish in ground color, those from the red 

 rocks are reddish, and those from the sand are sand-colored. 

 But these insects have fixed colors ; they cannot, like the 

 chameleon and certain other lizards, or like numerous small 

 fishes and some tree frogs, change color, quickly or slowly, 

 with changes in position that is, movements from green to 

 brown or to other colored environment. Variable protective 

 resemblance in insects is, as far as known, a variability directly 

 induced, to be sure, by varying environment, but all acquired 

 during the development of the individual insects, and fixed by 

 the time they reach the adult stage. But changes of color 

 to suit the changing surroundings can be quickly made in the 

 case of some animals. The chameleons of the tropics, whose 

 skin changes color momentarily from green to brown, blackish 

 or golden, is an excellent example of this highly specialized 

 condition. The same change is shown by a small lizard of our 

 Southern States (Anolius), which from its habit is called the 

 Florida chameleon. There is a little fish (Oligocottus) which 

 is common in the tide pools of the bay of Monterey, in Cali- 

 fornia, whose color changes quickly to harmonize with the 

 different colors of the rocks it happens to rest above. Most 

 of the tree frogs show this variable coloring. 



The well-known experiments of Trimen, Miiller, and Poulton 

 on the pupating larvae of swallow-tailed butterflies (Papilio), 

 and of Poulton on other butterflies of numerous species with 

 naked chrysalids, show that they take on the color, or a shade 

 resembling it, of the substance surrounding these larvse. They 

 show also that the result is due to a stimulus of the skin by the 

 enclosing color, and not to a stimulus received through the 

 eyes, and carried to the skin by the nerves. Larva? just ready 

 to pupate were enclosed in boxes lined with paper of different 

 colors ; the chrysalids w r hen formed were found to be colored to 

 harmonize with that particular shade of paper by which they 

 were surrounded while pupating. As these chrysalids in nature 

 hang exposed on bark and in other unsheltered places, without 

 protecting cocoon or cover of any kind, the actual protective 

 value of this harmonious coloration is obvious. It is a familiar 

 fact to entomologists that most butterfly chrysalids and naked 

 pupas of moths (unless concealed in the ground or elsewhere) 



