4 COLOR CHANGES IN ANIMALS 



mammals, with their coverings of feathers and of hairs 

 almost entirely lack this capacity. Among these forms 

 man, so far as I am aware, is the only species which in 

 a feeble way keeps up this type of reaction. Our facial 

 blush is dependent upon a temporary enlargement of the 

 small blood-vessels of the skin and corresponds in all 

 essential respects with the reddening of the integument 

 seen in such fishes as the top-minnows. But even this 

 mild activity, once such a powerful weapon in the hands 

 of the female of the species, will, I fear, soon find its 

 place among the lost arts, for the modern generation 

 seems to have given up a reaction-pattern that was at 

 once the charm and delight of an earlier day. 



Another all-important step taken by these older work- 

 ers was the discovery of the means by which color 

 changes were brought about. Over a century ago it 

 was found that those animals that show changes in tint 

 possess in their integuments a multitude of minute 

 bodies which by what appear to be contractions and 

 expansions are able to lighten, darken, or otherwise alter 

 the color of their possessors. These bodies were studied 

 in the cephalopods in 1819 by the Italian naturalist 

 Sangiovanni who called them cromofori, or in English 

 chromatophores. It is now known that chromatophores 

 are single integumentary cells or groups of such cells 

 containing pigment which by one means or another may 

 be concentrated and thus rendered inconspicuous, or 

 may be spread out and thus become exposed to view. 

 In the cephalopods, such as the octopus and the squid, 

 each chromatophore consists of a central elastic-walled 

 sac filled with pigment, around which is a system of 

 radiating muscle-fibers (Fig. 1). By means of these 

 fibers the spherical sac may be drawn out to a flattened 

 disc, thus spreading its pigment conspicuously, or it may 

 be allowed to contract to a minute sphere almost in- 



