8 THE EVOLUTION THEORY 



or from living on in a mutilated state, and in this lies an advantage 

 for the maintenance of the species, which is the greater the more 

 frequently injuries occur in the species, and the more they menace 

 its life directly or indirectly. A certain degree of regenerative 

 capacity is thus indispensable to all multicellular animals, even to 

 the highest among them. We ourselves, for instance, could not 

 escape the numerous dangers of infection by bacilli and other micro- 

 organisms if our protective outer skin did not possess the faculty 

 of regeneration, at least so far that it can close up a wound and 

 fill up with cicatrice -tissue a place where a piece of skin has been 

 excised. Obviously, then, the mechanism which evokes regeneration 

 must have been preserved in some degree and in some parts at every 

 stage of the phyletic development, and must have been strengthened 

 or weakened according to the needs of the relevant organism, being 

 concentrated in certain parts which were much exposed to injury 

 and withdrawn from other rarely threatened parts. Thus the great 

 diversity which we can now observe in the strength and localization 

 of the regenerative capacity has been brought about. But all this 

 can only be regarded as adaptation. 



I should like to submit a few examples to show that the 

 regenerative capacity is by no means uniformly distributed, and 

 that, as far as we can see, it is greater or less in correspondence 

 with the needs of the animal, both in regard to the whole and to 

 particular parts. 



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 I'egeneration, 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 begin- 

 ning of May I found on the walls of the harbour at Marseilles whole 

 forests of polyp-stocks of the genera Campanularia, Gonothyrcea, and 

 Ohelia, all large and splendidly developed, with thousands of indi- 

 vidual 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 givino- 

 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 



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