io THE CHARACTERS OF LIVING BEINGS 



advantageous to a deer, for example, to be able to heal a wound, 

 but the conditions of its life are such that it would very rarely have 

 time or opportunity to reproduce a lost limb. In effect the power 

 to do so would be useless. The stag, however, habitually re- 

 produces its lost antlers. They are very heavy structures which 

 are useful to him at the season when he contends with his rivals ; 

 but burdensome, and therefore, not only useless but worse than 

 useless, at other times. He sheds them, it is true, in the absence 

 of injury, but the whole process closely resembles loss and repro- 

 duction through injury, and demonstrates the difficulty of drawing 

 a sharply dividing line between nutriment and injury as stimuli. 



17. Some plants which sprang originally from germ-cells 

 multiply indefinitely by budding. Each bud is regarded by botan- 

 ists as a * person,' but a person in this sense is not quite the same 

 as an * individual ' which takes origin in a germ. Buds, even when 

 growing separated from the parent, are, in a real sense, portions of 

 the individual that rose from the germ. If we amputate the end 

 of a twig the injury may or may not heal as a scar, but the pro- 

 duction of buds is commonly increased. Are they to be regarded 

 as developing under the stimulus of nutriment, or of injury ? 

 Here again we see the close connexion between the power of 

 responding to the stimulus of nutriment and that of responding to 

 the stimulus of injury. Injury, indeed, may be regarded as one of 

 the conditions under which the stimulus of nutrition comes into 

 action. It awakens a power which has slumbered. 



1 8. Some animals lose living and active parts by injury almost 

 as regularly and replace them almost as readily as the stag his 

 antlers or the bear his winter coat. Thus in some newts the 

 external gills are much exposed and liable to be bitten off by 

 members of the same species. They are readily replaced, whereas 

 internal parts of the same animal show small powers of regenera- 

 tion': they merely heal. 1 Lizards which frequently escape from 

 enemies with the loss of the tail are able to reproduce it; but 

 they cannot reproduce a limb, the loss of which usually involves 

 capture and death. The power of regeneration 2 possessed by fishes 

 is apparently no greater than, if as great, as that possessed by 

 mammals. Some worms, much exposed to injury, are able to 



1 Weismann, Theory of Evolution, vol. ii. pp. 12-13. 



2 The term regeneration is usually limited to a more or less perfect replace- 

 ment of the lost part or tissues by similar structures ; whereas in mere healing 

 a scar, which may differ greatly from the lost part, is developed. The two 

 processes differ in degree, not in kind, and are united by gradations. Regeneration 

 is very perfect healing ; healing is imperfect regeneration. 



