It must first be pointed out that those lower Metazoa, like the Hydroid polyps in particular, which are endowed with such a high and general power of regeneration, do actually require this for their safety; they are not only soft, easily injured and torn, but they are most severely decimated by many enemies. In the beginning of May I found on the walls of the harbour at Marseilles whole forests of polyp-stocks of the genera _Campanularia_, _Gonothyræa_, and _Obelia_, all large and splendidly developed, with thousands of individual polyps and medusoids, but in a very short time the great majority of the polyps were eaten up by little spectre-shrimps (Caprellids) and other crustaceans, worms, and numerous other enemies, and towards the end of May it was no longer possible to find a fine well-grown colony. It must therefore be of decisive importance for these species if the stems and branches, which are spared because protected by horny tubes, possess the faculty of transforming their simple soft parts into polyp-heads, or of giving off buds which become polyps, or even of growing a new stock from the twigs which have been half-eaten and bitten loose from the stock and have fallen to the ground. If, finally, a torn-off polyp-stalk (of _Tubularia_) falls to the ground with the wrong side up, the end which is now the lower will send out roots, and the end now uppermost will give off a new head. This also appears to us adaptive, and does not surprise us, since we have been long accustomed to recognize that what is adapted to an end will realize this if it be possible at all. Think again of the innumerable adaptations in colour and form which we discussed in the earlier lectures. I hope later to be able to show in more detail how it comes to pass that necessity gives rise to adaptation. In regard to the case of the polyps, we can understand that, as far as a high degree of regeneration and budding was possible in these animals at all, it could not but be developed. Regeneration and budding complete each other in this case, for the former brings about in the individual 'person' what the latter does in the colony, namely, a _Restitutio in integrum_. It is readily intelligible that the former was not difficult to establish where the latter--the capacity of budding--was already in existence. It seems at first sight very striking that the higher plants, which all depend upon budding, and which form plant-colonies (corms) in the same sense as the polyps form animal-colonies, only possess the faculty of true regeneration in a very low degree, although they are extremely liable to injury.