All the birds, reptiles,
and insects of Sahara, says Canon Tristram, copy closely the grey or
isabelline colour of the boundless sands that stretch around them. Lord
George Campbell, in his amusing 'Log Letters from the "Challenger,"'
mentions a butterfly on the shore at Amboyna which looked exactly like a
bit of the beach, until it spread its wings and fluttered away gaily to
leeward. Soles and other flat-fish similarly resemble the sands or banks
on which they lie, and accommodate themselves specifically to the
particular colour of their special bottom. Thus the flounder imitates
the muddy bars at the mouths of rivers, where he loves to half bury
himself in the congenial ooze; the sole, who rather affects clean hard
sand-banks, is simply sandy and speckled with grey; the plaice, who goes
in by preference for a bed of mixed pebbles, has red and yellow spots
scattered up and down irregularly among the brown, to look as much as
possible like agates and carnelians: the brill, who hugs a still rougher
ledge, has gone so far as to acquire raised lumps or tubercles on his
upper surface, which make him seem like a mere bit of the shingle-strewn
rock on which he reposes. In short, where the environment is most
uniform the colouring follows suit: just in proportion as the
environment varies from place to place, the colouring must vary in order
to simulate it. There is a deep biological joy in the term
'environment'; it almost rivals the well-known consolatory properties of
that sweet word 'Mesopotamia.
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