Regeneration, on Weismann’s view, is brought about by latent cells containing pre-formed germs in the chromosomes of the nucleus. These germs are called the determinants. Since at each level in an animal, or in a part of an animal, regeneration may occur and replace the missing part, it is assumed that the germs are correspondingly 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 regeneration 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 adaptation_.” Again, “Hence there is no such thing as a general power of regeneration; in each kind of animal this power is graduated according 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.