THE power of regeneration already noted in some of the lower animals is present to a considerable extent in many of the Echinoderms. The sea-cucumbers are close relatives of the starfish but have plump, elongated bodies covered with a warty skin and look, in fact, like cucumbers except in colour.
They, too, have longitudinal rows of tube-feet running along the body. Their mere appearance is sufficiently repulsive, but their methods of protecting themselves are even more to be deplored. An irritated sea-cucumber will not hesitate to eject the whole of its internal organs, an evil-smelling mass, squirting them at whoever may be the cause of the annoyance. Such wholesale self-mutilation is not so injurious as might appear to be the case since the sea-cucumber is able to regenerate all the lost parts in a short space of time. Starfish, also, have been known to eject the whole of their digestive organs when they have swallowed something that does not agree with them, and to re-grow the lost organs—a truly novel cure for indigestion!
The occasions when such drastic remedies for mistakes in diet are necessary are probably few and far between. On the other hand, the ability to repair and replace lost limbs is an ever-present need with starfish, owing to the depredations of crabs of all sizes and descriptions, who do not hesitate to attack a starfish, wrench off a portion of one of its arms and depart to enjoy the feast at leisure. Starfish may often be found in which the arms bear as many as a dozen or more scars, each scar representing an occasion on which a part or the whole of an arm has been lost and has been replaced. How great is this power of replacement may be judged from the fact that so long as the central disc and one arm remain intact the other four arms may be damaged again and again, and as often replaced, without causing the animal’s death or causing, so far as can be ascertained, any great inconvenience.