Page:Popular Science Monthly Volume 75.djvu/345

Rh intimate relations to the successful action of such an organ as an eye, and yet with complete independence of central-nervous control. Other chromatophores, like those in the skin of lizards, can be as clearly demonstrated to be under the control of nerves as those in the eyes of Palæmonetes have been shown to be free from this control. The integumentary color changes in lizards are often extremely complicated processes, especially in such forms as the chameleon, but they include as a fundamental principle the inward and outward migration of dark pigment-granules within certain large unicellular chromatophores (Fig. 2). When these pigment-granules pass out into the processes of the chromatophores, they give to the surface of the lizard a dark or even black aspect. When they migrate inward to the body of the chromatophore,

 showing the condition due to the dark (A) and to the light (B). c, chromatophore; d, derma; e, epidermis; g, irregular masses of ground color.

which is often hidden in pigment masses of some particular color, they thus allow the ground-color behind them to assert itself. By this simple inward and outward migration of the pigment, the chief change in the color differences of the lizard's skin is accomplished. The question that we have to consider is to what extent these changes are controlled by the central nervous organs.

The inward and outward migration of the pigment of the chromatophores is well seen in the skin of the so-called Florida chameleon, Anolis. According to Carlton (1903), who has studied this animal with care, the passive state in its chromatophores is that in which their pigment is gathered together in the cell-bodies. This state is brought about when the lizard is removed from the stimulating effect of light, when the blood and nerve supply of a given region are cut off, when the animal is etherized, or when it dies. In fact any change that might be expected to interfere with nervous activity calls forth this condition. Since nicotine is a poison for the sympathetic nervous system, rendering it temporarily inactive, and since the inward migration of the chromatophoral pigment is immediately produced on injecting a very small amount of nicotine into the Anolis, it is probable that the reverse process, the outward migration, is dependent upon the normal action of