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 fish similarly alter their colour to suit
their background 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 environment 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
complex.
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