If you divide the little fresh-water polyp Hydra fusca in two, even if you do it very unsymmetrically so that one part gets all the tentacles and the other part none, both parts will develop into complete, slightly smaller specimens of Hydra; and that game can be played repeatedly (Verworn, Allgemeine Physiologie, chap, I; Fischer: Jena, 1915). This is by no means a unique case amongst organisms at this level; R. Semon (Mneme, 2nd ed., p. 151) reports the same thing of Planaria, amongst others. His special interest in the matter is that he sees this reproduction of the missing part, not unreasonably, as strictly analogous to associative reproduction in the higher kinds of memory. In the same way Semon sees the recapitulation of the whole evolutionary process, which regularly takes place in the higher animals and plants from the embryonic stage upwards, as parallel to the recapitulation of a poem learnt by heart: and this not as a metaphor, but in the real sense that both phenomena are to be subsumed under the higher concept for which he uses the word ‘mnemic’.