262 KE GENEKA TION 



These germs are called the determinants. Since at each level in an 

 animal, or in a part of an animal, regeneration may occur and re- 

 place the missing part, it is assumed that the germs are correspond- 

 ingly different at each level, and represent all the parts that lie 

 distal to that region. Weismann does not suppose that there is a 

 single germ at each level that represents all the distal parts, but that 

 in each layer, or organ, or part there are many cells that contain 

 germs corresponding to the distal regions. The qualities of the 

 latent cells are sorted out by means of the qualitative divisions of the 

 chromatic material of the nucleus. Moreover, since the new part can 

 itself regenerate, the further assumption is made that during regen- 

 eration new subsidiary or latent cells are laid down at each level. 

 This is supposed to be brought about by a quantitative division of 

 each germ after it has reached its definitive position in the new part. 



Weismann's general attitude toward the problem of regeneration 

 is summed up in the following statements : " It may, I believe, be 

 deduced with certainty from those phenomena of regeneration with 

 which we are acquainted, that the capacity for regeneration is not a 

 primary quality of the organism, but that it is a phenomenon of adap- 

 tation." Again, " Hence there is no such thing as a general power 

 of regeneration ; in each kind of animal this power is graduated ac- 

 cording to the need of regeneration in the part under consideration." 

 " 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 has slowly 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 at the 

 same time frequently exposed to loss." 



The evidence brought forward in the preceding pages leads, I 

 think, to precisely the opposite conclusions, and, in certain cases at 

 least, it has been shown that there can be no relation between the 

 power of regeneration and the extent of exposure of a part to injury 

 or to loss. It is unnecessary to enter here further into this question, 

 since it has been discussed already in Chapter V. 



Weismann's statement that the power of regeneration has de- 

 creased " in correspondence with the increase in the complexity of the 

 part" cannot by any means be entirely accepted. If the complexity 

 of a part is of such a kind that the part cannot sustain itself indepen- 

 dently until regeneration has taken place, or if the exposed surface of 

 the wound is such that it cannot be closed over, or if the new part 

 cannot be properly nourished, or if the tissues have changed in such 

 a way that their cells can no longer multiply, then the statement is, to 



