withered leaves, these creatures change color, putting on a grayish and brownish coat of hair. The ptarmigan of the Rocky 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 little fish (Oligocottus snyderi) which is common in the tide pools of the bay of Monterey, in California, whose color changes quickly to harmonize with the different colors of the rocks it happens to rest above. Some of the treefrogs show this variable coloring. A very striking instance of variable protective resemblance is shown by the chrysalids of certain butterflies. uralist collected many caterpillars of a certain species of

An eminent English nat

butterfly, and put them, just as they were about to change into pupa or chrysalids, into various boxes, lined with paper of different colors. The color of the chrysalid was found

to harmonize very plainly with the color of the lining of the box in which the chrysalid hung. It is a familiar fact to entomologists that most butterfly chrysalids resemble in

color and general external appearance the surface of the object on which they rest (Figs. 214 and 215).

sum.

282. Special protective resemblance.-Far more striking are those cases of protective resemblance in which the animal resembles in color and shape, sometimes in extraordinary detail, some particular object or part of its usual environment. Certain parts of the Atlantic Ocean are covered with great patches of sea-weed called the gulf-weed (Sargassum), and many kinds of animals-fishes and other creatures-live upon and among the alga. No one can fail to note the extraordinary color resemblances which exist between those animals and the weed itself. The gulf-weed is of an olive-yellow color, and the crabs and shrimps, a certain flat-worm, a certain mollusk, and a little fish, all of which live among the Sargassum, are exactly of the same. shade of yellow as the weed, and have small white markings on their bodies which are characteristic also of the SargasThe mouse-fish or Sargassum fish and the little seahorses, often attached to the gulf-weed, show the same traits of coloration. In the black rocks about Tahiti is found the black noki or lava-fish (Emmydrichthys vulcanus) (Fig. 167), which corresponds perfectly in color and form to a piece of lava. This fish is also noteworthy for having envenomed spines in the fin on its back. The slender grass-green caterpillars of many moths and butterflies resemble very closely the thin grass-blades among which they live. The larvæ of the geometrid moths, called inch-worms or span-worms, are twig-like in appearance, and have the habit, when disturbed, of standing out stiffly from the twig or branch upon which they rest, so as to resemble in position as well as in color and markings a short or a broken twig. One of the most striking resemblances of this sort is shown by the large geometrid larva illustrated in Fig. 216, which was found near Ithaca, New York. The body of this caterpillar has a few small, irregular spots or humps, resembling very exactly the scars left by fallen

buds or twigs. These caterpillars have a special muscular development to enable them to hold themselves rigidly for

middle prop-legs of the body, common to other lepidopter

ous larvæ, the presence of which would tend to destroy the illusion so successfully carried out by them. The common walking-stick (Diapheromera) (Fig. 217), with its wingless, greatly elongate, dull-colored body, is an excellent example of special protective resemblance. It is quite indistinguishable, when at rest, from the twigs to which it is clinging. Another member of the family of insects to which the walking-stick belongs is the famous green-leaf insect (Phyllium)

(Fig. 218). It is found in South America and is of a bright green color, with broad leaf-like wings and body, with markings which imitate the leaf veins, and small irregular yellowish spots which mimic decaying or stained or fungus-covered spots in the leaf.

There are many butterflies that resemble dead leaves. All our common meadow browns (Grapta), brown and reddish butterflies with ragged-edged wings, that appear in the autumn and flutter aimlessly about exactly like the falling leaves, show this resemblance. But most remarkable of all is a large butterfly (Kallima) (Fig. 219) of the East Indian region. The upper sides of the wings are dark, with purplish and orange markings, not at all resembling a dead leaf. But the butterflies when at rest hold their wings together over the back, so that only the under sides of the wings are exposed. The under sides of Kallima's wings are exactly the color of a dead and dried leaf, and