422 Dynamic Theory. 



uralists, that animals are often like their surroundings in color. Thus 

 the ' ' inhabitants of the deserts, the Jerboa, or leaping mice, Foxes of 

 the desert, Gazelles, Lions, &c. , are mostly of a yellow or yellowish- 

 brown color, like the sand of the desert. The polar animals, which live 

 surrounded by snow and ice, are white or gray. Many animals change 

 their color in summer and winter, getting gray or blackish in summer, 

 and white in winter. Many insects, like plant lice. &c. , living on green 

 leaves, are green, others, like butterflies of gay color, hover about 

 bright colored flowers. 



Haeckel also observes that many sea animals are bluish or completely 

 colorless and transparent, like the water they live in. Certain fish 

 the Helmicthyidae are so transparent that a book can be read through 

 their bodies. Then there are, among the mollusks, the finned snails 

 (Heteropods) and sea butterflies (Pteropods) ; among worms, the Sal- 

 pse, Alciope, and Sagitta ; among the Crustacea, a great many crabs ; 

 among the Co3lenterates, the most of the jelly fishes, &c. , all of which, 

 living on or near the surface of the water, are transparent and without 

 color, while their relatives of close kin, which live at the bottom of the 

 ocean, are colored and opaque, like animals on land. 



Everybody agrees with Darwin, that natural selection has much to do 

 with the preservation of those animals whose color most tends to make 

 them inconspicuous, but it does not account for the diversity of color- 

 ing in the first place. Without doubt the plastic tissues of the organ- 

 ism are directly affected by the reflections of light from their surround- 

 ings. In some cases, especially among the lowest, it is a mere matter 

 of food. A worm consisting of a transparent skin, stuffed with green 

 food, might easily be green, and a medusa composed of 99 per cent, 

 clear water, might easily be transparent, while another, living on muddy 

 water, might have a muddy hue. But the color of the white bear, and 

 the winter bleaching of rabbits,* and other animals, must be due to the 

 influence of prevailing colors in their environment. 



At the same time we must not lose sight of the fact that where the 

 coloring of the environment consists largely of color in plants, that cir- 

 cumstance shows that something in their environment colors them ; and 

 we may suppose that what colors them, might also give animals their 

 color. Of course the animal is plastic as well as the vegetable, and af- 

 fected by the same phases of energy. The vegetable is, however, first 

 in point of time and so must contribute to the influences which operate 

 on the animal. Where all light is excluded, organic tissues are apt to 

 be white or light colored. Plants raised in the dark are colorless, and 

 in colored animals those parts which are most sheltered from the rays 

 of the sun are apt to remain uncolored. This is the case with fish which 

 are colored on the back but white on the belly ; also deer and antelope, 



