STRICTLY INCOG. 69 



rest. On a sandy bottom it appears grey or sand-coloured ; 

 when lurking among seaweed it becomes green, or red, or 

 brown, according to the nature of its momentary back- 

 ground. Probably the effect is quite unconscious, or at 

 least involuntary, like blushing with ourselves — and nobody 

 ever blushes on purpose, though they do say a distinguished 

 poet once complained that an eminent actor did not follow 

 his stage directions because he omitted to obey the rubrical 

 remark, ' Here Harold purples with anger.' The change 

 is produced by certain automatic muscles which force up 

 particular pigment cells above the others, green coming to 

 the top on a green surface, red on a ruddy one, and brown 

 or grey where the circumstances demand them. Many 

 kinds of fisli similarly alter their colour to suit their back- 

 ground by forcing forward or backward certain special 

 pigment- cells known as chromatophores, whose various 

 combinations produce at will almost any required tone or 

 shade. Almost all reptiles and amphibians possess the 

 power of changing their hue in accordance with their en- 

 vironment in a very high degree ; and among certain tree- 

 toads and frogs it is difficult to say what is the normal 

 colouring, as they vary indefinitely from buff and dove- 

 colour to chocolate-brown, rose, and even lilac. 



But of all the particoloured reptiles the chameleon is by 

 far the best known, and on the whole the most remarkable 

 for his inconstancy of coloration. Like a lacertine Vicar 

 of Bray, he varies incontinently from buff to blue, and from 

 blue back to orange again, under stress of circumstances. 

 The mechanism of this curious change is extremely com- 

 plex. Tiny corpuscles of different pigments are sometimes 

 hidden in the depths of the chameleon's skin, and some- 

 times spread out on its surface in an interlacing network of 

 brown or purple. In addition to this prime colouring 

 matter, however, the animal also possesses a normal yellow 



