ORIGIN OF THE NERVOUS SYSTEM 341 



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 Palcemonetes 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 chro- 



A B 



Fig. 2. Two Chroiiatopeores from the Skin of a Lizard, showing the con- 

 dition due to the dark (A) and to the light (B). c, chromatophore ; d, derma; e, 

 epidermis ; g, irregular masses of ground color. 



matophore, 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 chromato- 

 phores 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, render- 

 ing it temporarily inactive, and since the inward migration of the chro- 

 matophoral 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 



