Hardly any other vertebrate has attained such celebrity on account of its high regenerative capacity as the water-newt, species of the genus _Triton_. It can regrow not only its tail, but the legs and their parts if they are cut off. Spallanzani saw the legs grow six times, after he had cut them off six times. In the blind newt (_Proteus_) of the Krainer caves, a near relative of the common newt, the leg regenerated only after a year and a half, although the animal stands on a lower stage of organization than the newt, and thus should rather replace lost parts more easily. But Proteus lives sheltered from danger in dark, still caves, while Triton is exposed to numerous enemies which bite off pieces from its tail or legs; and the legs are its chief means of locomotion, without which it would have difficulty in procuring food. It is different with the elongated eel-like newt of the marshes of South Carolina, _Siren lacertina_. This animal moves by wriggling its very muscular trunk, after the manner of an eel, and in consequence of the disuse of its hind legs it has almost completely lost them. Even the fore-legs have become small and weak, and possess only two toes, and these do not regrow if they are bitten off, or only do so very slowly. Earthworms are exposed to much persecution; not only birds, such as blackbirds and some woodpeckers, but, above all, the moles prey upon them, and Dahl has shown that moles often lay up stores of worms in winter which they have half crippled by a bite, while even Réaumur knew that moles frequently only half devoured earthworms. It was thus an obvious advantage to earthworms that a part of the animal should be able to regrow a whole, and accordingly we find a fairly well-developed regenerative capacity among them. But it varies greatly in the different species, and it would be interesting if we knew the conditions of life well enough to be able to decide whether the faculty of regeneration rises and falls in proportion to the dangers to which the species is exposed. Unfortunately we are far from this as yet; we only know that, in the common earthworms of the genera _Lumbricus_ and _Allolobophora_, the faculty of regeneration is still very limited, for at most two worms, and sometimes only one, can develop from an animal cut into two pieces. Cutting into a greater number of pieces does not yield a larger number of worms, but usually only one, and often none at all.