to circumstances.  In proportion as it presents a strikingly vivid or distinct appearance among the surrounding sand will it make itself a sure mark for its watchful foes, if it happen to be an unprotected skulker, or will it be seen beforehand and avoided by its prey, if it happen to be a predatory hunting or insect-eating beast.  Hence on the sandy desert all species alike are uniformly sand-coloured.  Spotty lizards bask on spotty sands, keeping a sharp look-out for spotty butterflies and spotty beetles, only to be themselves spotted and devoured in turn by equally spotty birds, or snakes, or tortoises.  All nature seems to have gone into half-mourning together, or, converted by a passing Puritan missionary, to have clad itself incontinently in grey and fawn-colour.

Even the larger beasts that haunt the desert take their tone not a little from their sandy surroundings.  You have only to compare the desert-haunting lion with the other great cats to see at once the reason for his peculiar uniform.  The tigers and other tropical jungle-cats have their coats arranged in vertical stripes of black and yellow, which, though you would hardly believe it unless you saw them in their native nullahs (good word ‘nullah,’ gives a convincing Indian tone to a narrative of adventure), harmonise marvellously with the lights and shades of the bamboos and cane-brakes through whose depths the tiger moves so noiselessly.

Looking into the gloom of a tangled jungle, it is almost impossible to pick out the beast from the yellow stems and dark shadows in which it hides, save by the baleful gleam of those wicked eyes, catching the light for one second as they turn wistfully and bloodthirstily towards the approaching stranger.  The jaguar, oncelot, leopard, and other tree-cats, on the other hand, are dappled or spotted—­a type of coloration which exactly harmonises with the light and shade of the round sun-spots seen through the foliage of a tropical forest.  They, too, are almost indistinguishable from the trees overhead as they creep along cautiously on the trunks and branches.  But spots or stripes would at once betray the crouching lion among the bare rocks or desert sands; and therefore the lion is approximately sand-coloured.  Seen in a cage at the Zoo, the British lion is a very conspicuous animal indeed; but spread at full length on a sandy patch or among bare yellow rocks under the Saharan sun, you may walk into his mouth before you are even aware of his august existence.

The three other great desert beasts of Asia or Africa—­the ostrich, the giraffe, and the camel—­are less protectively coloured, for various reasons.  Giraffes and ostriches go in herds; they trust for safety mainly to their swiftness of foot, and, when driven to bay, like most gregarious animals, they make common cause against the ill-advised intruder.  In such cases it is often well, for the sake of stragglers, that the herd should be readily distinguished at a