REGENERATION AND LIABILITY TO INJURY IO/ 



possess remarkable powers of regeneration. There are a few very 

 dubious observations in regard to the regeneration in man of super- 

 fluous digits that had been cut off. 1 



These examples might be added to by others in the groups cited, 

 and also by examples taken from the smaller groups of the animal 

 kingdom, but those given will suffice, I think, to show that the power 

 to regenerate is characteristic of entire groups rather than individual 

 species. When exceptions occur, we do not find them to be forms 

 that are obviously protected, but the lack of regeneration can rather 

 be accounted for by some peculiarity in the structure of the animal. 

 If this is borne in mind, as well as the fact that protected and unpro- 

 tected parts of the same animal regenerate equally well, there is 

 established, I think, a strong case in favor of the view that there is 

 no necessary connection between regeneration and liability to injury. 

 We may therefore leave this side of the question and turn our atten- 

 tion to another consideration. 



It will be granted without argument that the power of replacement 

 of lost parts is of use to the animal that possesses it, especially if the 

 animal is liable to injury. Cases of usefulness of this sort are gener- 

 ally spoken of as adaptations. The most remarkable fact in connec- 

 tion with these adaptive responses is that they take place, in some 

 cases at least, in parts of the body where they can never, or at most 

 very rarely, have taken place before, and the regeneration is as per- 

 fect as when parts liable to injury regenerate. Another important 

 fact is that in some forms the regeneration is so slow that if the 

 competition amongst the animals was very keen those with missing 

 legs, or eyes, or tails, would certainly succumb ; yet, if protected, they 

 do not fail to regenerate. If, therefore, the animal can exist through 

 the long interval that must elapse before the lost part regenerates, 

 we cannot assume that the presence of the part is of vital importance 

 to the animal, and hence its power to regenerate could scarcely be 

 described as the result of a "battle for existence," and without this 

 principle " natural selection " is powerless to bring about its supposed 

 result. 



It is extremely important to observe that some cases, at least, of 

 regeneration are not adaptive. This is shown in the case where a new 

 head regenerates at the posterior end of. the old one in P lamina 

 htgubris, or where a tail develops at the anterior end of a posterior 

 piece of an earthworm, or when an antenna develops in place of an 

 eye in several Crustacea. If we admit that these results are due to 

 some inner laws of the organism, and have nothing to do with the rela- 

 tion of the organism to its surroundings, may we not apply the same 

 principle to other cases of regeneration in which the result is useful ? 



1 See Darwin, loc cit. 



