BODILY CHARACTERISTICS INCONSPICUOUSNESS 291 



clear that the colour effect will vary according to the number 

 which are at a given time in a relaxed condition, and the depth 

 in the skin at which these are situated. And it has further 

 been proved that the eyes of the animal must be uninjured if the 

 hues of the body are to be adjusted, so that the colours of the 

 surroundings first affect the visual organs, from which nervous 

 impulses are carried to the brain and thence in a roundabout 

 way to the skin. It will readily be perceived that a case like 

 this presents a physiological problem of no little complexity, the 

 nature of which has only been indicated. It may be here re- 

 marked that though the Chameleon is the most striking example 

 among the Reptiles of colour-change, it is by no means the sole 

 member of that class which illustrates the phenomenon. 



COLOUR-CHANGE IN AMPHIBIANS. Some familiar Amphibians 

 vary in colour according to the surroundings, though not so 

 rapidly as the last-named animal, and the nature and causes of 

 the change are substantially the same. Our Common Frog (Rana 

 temporaria] has been the subject of careful investigations in this 

 respect. It is quite easy to produce the change in a captive 

 specimen. If placed for a short time in a dark box it will assume 

 a blackish appearance, and if then transferred to fresh damp grass 

 and placed in a bright place it will speedily take on a yellowish- 

 green tint. The arrangement is obviously protective, but it may 

 be aggressive as well, for insects form a large part of the food, 

 and a good dinner may depend upon approaching them unobserved 

 until the long tongue can be shot out with a good chance of catch- 

 ing them (see p. 82). 



COLOUR-CHANGE IN FISHES. Fishes, especially those which 

 are ground-feeders, possess in many if not all cases a power of 

 colour-adjustment, the mechanism being the same as in Reptiles 

 and Amphibia. The protective arrangements in Flat- Fishes have 

 already been noted (p. 284), but probably the description might 

 have been given with greater propriety under the present heading. 

 Plaice, for example, are known to be able to vary their prevailing 

 hue according as the surrounding part of the sea-bottom is light 

 or dark, and a very interesting observation was made many years 

 ago upon a number of these fishes which at the time were resting 

 upon white sand. With the exception of one specimen they had 

 all assumed a light colour, and on closer examination that par- 

 ticular fish proved to be blind, and therefore did not possess the 



