PROTECTIVE RESEMBLANCES, AND MIMICRY 353 



withered leaves, these creatures change color, putting on 

 a grayish and brownish coat of hair. The ptarmigan of 

 the Eocky Mountains (one of the grouse), which lives on 

 the snow and rocks of the high peaks, is almost wholly 

 white in winter, but in summer when most of the snow is 

 melted its plumage is chiefly brown. On the campus at 

 Stanford University there is a little pond whose shores are 

 covered in some places with bits of bluish rock, in other 

 places with bits of reddish rock, and in still other places 

 with sand. A small insect called the toad-bug ( Galgulus 

 oculatus) lives abundantly on the banks of this pond. 

 Specimens collected from the blue rocks are bluish in 

 color, those from the red rocks are reddish, and those from 

 the sand are sand-colored. Such 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 lit- 

 tle fish (Oligocottus snyderi) 

 which is common in the tide 

 pools of the bay of Monterey, 

 in California, whose color 

 changes quickly to harmo- 

 nize with the different colors 

 of the rocks it happens to 

 rest above. Some of the tree- 

 frogs show this variable col- 

 oring. A very striking in- 

 stance of variable protective 

 resemblance is shown by the 

 chrysalids of certain butterflies. An eminent English nat- 

 uralist collected many caterpillars of a certain species of 



PIG. 214. Chrypalid of swallow-tail but- 

 terfly (Papilio), harmonizing with the 

 bark on which it rests. 



