A coral reef is gorged with a population of varied elements viciously disposed towards each other.  It is one of Nature’s most cruel battlefields, for it is the brood of the sea that “plots mutual slaughter, hungering to live.”  Molluscs are murderers and the most shameless of cannibals.  No creature at all conspicuous is safe, unless it is agile and alert, or of horrific aspect, or endowed with giant’s strength, or is encased in armour.  A perfectly inoffensive crab, incapable of inflicting injury to anything save creatures of almost microscopic dimensions, assumes the style and demeanour of a ferocious monster, ready at a moment’s notice to cry havoc, and let loose the dogs of war.  Another hides itself as a rugged nodule of moss-covered stone; its limbs so artfully stowed away that detection would be impossible did it not occasionally betray itself by a stealthy movement.  The pretty cowrie, lemon-coloured and grey and brown, throws over its shining shoulders a shawl of the hue of the rock on which it crawls about, grey or brown or tawny, with white specks and dots which make for invisibility—­a thin filmy shawl of exquisite sensitiveness.  Touch it ever so lightly, and the helpless creature, discerning that its disguise has been penetrated, withdraws it, folding it into its shell, and closes its door against expected attack.  It may feebly fall off the rock, and simulating a dead and empty shell, lie motionless until danger is past.  Then again it will drape itself in its garment of invisibility and slide cautiously along in search of its prey.  Under the loose rocks and detached lumps of coral for one live there will be scores of dead shells.  The whole field is strewn with the relics of perpetual conflict, resolving and being resolved into original elements.  We talk of the strenuous life of men in cities.  Go to a coral reef and see what the struggle for existence really means.  The very bulwarks of limestone are honeycombed by tunnelling shells.  A glossy black, torpedo-shaped creature cuts a tomb for itself in the hard lime.  Though it may burrow inches deep with no readily visible inlet, cutting and grinding its cavity as it develops in size and strength, yet it is not safe.  Fate follows in insignificant guise, drills a tiny hole through its shell, and the toilsomely excavated refuge becomes a sepulchre.  Even in the fastness of the coral “that grim sergeant death is strict in his arrest.”  All is strife—­war to the death.  If eternal vigilance is the price of liberty among men, what quality shall avert destruction where insatiable cannibalism is the rule.  There is but one creature that seems to make use of the debris of the battlefield—­the hermit crab (CAENOBITA), which but half armoured must to avert extermination fit itself into an empty shell, discarding as it grows each narrow habitation for a size larger.  Disconsolate is the condition of the hermit crab who has outgrown his quarters, or has been enticed from them or “drawn” by