REGENERATION AND LIABILITY TO INJURY 95 



which is to some extent unforeseen of the physical nature of an 

 animal. Some statements which have been made on this subject seem 

 hardly to admit of any but the latter explanation." After showing that 

 some newts confined in aquaria attacked each other, " and several 

 times one of them seized another by the lower jaw, and tugged and 

 bit at it so violently that it would have been torn off had I not separated 

 the animals" 1 and after referring to the regeneration of the stork's 

 beak, Weismann concludes: " Such cases, the accuracy of which can 

 scarcely be doubted, indicate that the capacity for regeneration does not 

 depend only on the special adaptation of a particular organ, but that 

 a general power also exists which belongs to the whole organism, and 

 to a certain extent affects many and perhaps even all parts. By 

 virtue of this power, moreover, simple organs can be replaced when 

 they are not specially adapted for regeneration." The perplexity of 

 the reader, as a result of this temporary vacillation on Weismann's 

 part, is hardly set straight by the general conclusion that follows on 

 the same page : " We are, therefore, led to infer that the general 

 capacity of all parts for regeneration may have been acquired by 

 selection in the lower and simpler forms, and that it gradually 

 decreased in the course of phylogeny in correspondence with the 

 increase in complexity .of organization ; but that it may, on the other 

 hand, be increased by special selective processes in each stage of its 

 degeneration, in the case of certain parts which are physiologically 

 important and are at the same time frequently exposed to loss." 



There are certain statements of facts in the same chapter that are 

 incorrect, and the argument is so loose and vague that it is difficult 

 to tell just what is really meant. As a misstatement of fact I may 

 select the following case : It is stated that lumbriculus does not have 

 the power of regenerating laterally if cut in two, and it is argued that 

 a small animal of this form could rarely be injured at the side without 

 cutting the animal completely in two. As a matter of fact, lumbricu- 

 lus can regenerate laterally, and very perfectly, as any one can verify 

 if he takes the trouble to perform the experiment ; but, of course, if 

 the whole animal is split in two lengthwise the pieces die, or if a very 

 long piece is split from one side the remaining piece usually disin- 

 tegrates. If, however, the anterior end is split in two for a short 

 distance, or if a piece is partially split in. two, the half remaining in 

 contact with the rest of the piece completes itself laterally. The 

 same result follows also in the earthworm. 



As an example of looseness of expression I may quote the follow- 

 ing from Weismann : "A useless or almost useless rudimentary part 

 may often be injured or torn off without causing processes of selection 

 to occur iv/iich would produce in it a capacity for regeneration. The 



1 The italics are, of course, my own. T. H. M. 



