INSTINCTIVE, EMOTIONAL AND REFLEX ACTION 335 



change in crustaceans. According to these authors the 

 pigment cells can, as a rule, be considered as consisting 

 of a central body from which a system of more or less 

 complicated ramifications or processes spreads out in 

 all directions. As a rule, the center of the cell contains 

 one or more different pigments which, under the influence 

 of nerves, can spread out separately or together into the 

 ramifications. These phenomena of spreading and retrac- 

 tion of the pigments into or from the ramifications of the 

 pigment cells, form on the whole the basis for the color 

 changes. Under the influence of environment, when the 

 animal appears transparent, all the pigment is contained 

 in the middle of the cell while the ramifications are free 

 from pigment. When the animal appears brown both 

 pigments are spread out into ramifications. In the con- 

 dition of normal spreading the animals appear black, 

 while many animals show transitory changes in color 

 under influence of their surroundings ; in a few cases 

 permanent changes can be produced. 



"The best examples of this are those observed by Paul- 

 ton, in the chrysalids of various butterflies. These ex- 

 periments are so well known that a short reference to 

 them will be sufficient. Paulton found that in gilt or 

 white surroundings the pupae became light colored and 

 there was often an immense development of the golden 

 spots so that in many cases the whole surface of the 

 pupae glittered with an apparent metallic luster. So 

 remarkable was the appearance that a physicist to whom 

 I showed the chrysalids suggested that I had played a 

 trick and had covered them with gold leaf. When black 

 surroundings were used they were as a rule extremely 

 dark." 



Just notice the facts in these cases : first, a picture of 

 the ground is taken in the eye, transferred to the skin 



