Another group of worm-like or snaky creatures common on a coral-reef are the sea-cucumbers or bêche-de-mer. In my experience the most singular branch of the family is at once the longest and thinnest, for it resembles a snake so closely that at first sight the observer subconsciously assumes an attitude of hostility. There seem to be two varieties of the species. One is much more ruddy in appearance than the other, and its body is the smoother; but they are much alike in physique and helplessness. The figure of a sausage-skin four or five and even six feet long, and capable of elongation to almost double, containing muddy water in circulation and one end exhibiting a set of ever-waving tentacles, conveys a not unflattering notion of the animal as it lies coiled among the coral, half hidden with algae. Far too feeble to be offensive, it suffers collapse on alarm--that is to say, if such a violent mental and physical ill can befall an animal of such crude organism. At least, the tentacles are withdrawn, nor will they be protruded until some sense--unlikely to be either sight, hearing, taste, or touch, but probably nervous tension acutely susceptible to vibrations--tells that danger is past. Then the tentacles are shyly exhibited and the agitations of the animal are renewed. Throughout the length of the body of the more remarkable of the two species of which I may speak on first-hand knowledge are four rows of bosses, closely spaced, which when the animal has dragged its slow length along to the utmost limit diminish into mere wrinkles, and disappear altogether when it is slung across a stick, and the fluid contents, being precipitated, congest and woefully weight each end, sometimes to the bursting-point. The bosses of repose seem to indicate so much length in reserve. A dozen simple tentacles, sword-shaped, with frayed edges, and about an inch and a half long, indicate the head without decorating it, for they are of an inconspicuous neutral tint, closely resembling the alga among which the animal slowly winds its way.