1899] REGENERATION 323 



only one possible answer to this question, viz. because the " Anlagen " 

 are not there. 



The facts recently established certainly indicate that, at any rate 

 among many animals, the embryo and the young organism possess 

 many cells whose wealth of " Anlagen " can, under the determining 

 guidance of the whole, bring about the regeneration of parts in different 

 directions ; but it seems to me equally certain that, as the organism 

 approaches maturity, the number of such cells gradually decreases, and 

 the potentiality of their " Anlagen " becomes gradually more restricted, 

 until, finally, many cells are only able to reproduce their like. But 

 how far this limiting of the "' Anlagen " goes, and how far the cell 

 contains inactive " Anlagen " (" Neben-Determinanten "), is obviously 

 determined by the necessities of the case, and depends on adaptation ; 

 in so far, at least, it will hardly be disputed that the capacity for 

 the regeneration of parts is regulated by adaptation. It is impossible 

 to say whether we must not go much farther than this, and regard the 

 power of the blastomeres to produce the whole as a very ancient but 

 nevertheless secondary phenomenon, depending on adaptation to injury. 

 But if we bear in mind how the differentiation between homoplastids 

 and heteroplastids occurs in the Volvocidae, it is evident that the first 

 separation of the germ-cells and the body-cells in this case cannot be 

 referred to different liberating stimuli, but must consist in a separation 

 of the " Anlagen " ; the latter must therefore be the primary arrange- 

 ment, and the equipment of the blastomeres with the whole germ-plasm 

 only a secondary acquisition. We thus once more arrive at the view, 

 adopted both by Eoux and myself, of " reserve germ-plasm " — of 

 supplementary germ-plasm in general, — with which Barfurth also agrees. 



To this important point, too, I hope to return at a future time, 

 when I intend to reply to the factual criticisms of my opponents. 

 This short essay owes its origin to purely external reasons, and I have 

 written it rather for the supporters than for the opponents of my views, 

 and rather to show that the recently established facts harmonise well 

 with the fundamental principles of my theory than to meet the objec- 

 tions of my antagonists in detail. To reply to the many invectives, 

 the sarcasm and derision which have been showered upon me in such 

 overflowing measure since the publication of the " Germ-Plasm " seems 

 to me quite superfluous, for I regard such utterances as a not exactly 

 desired, but yet a not altogether unsatisfactory sign, that the less noble 

 emotions of human nature — envy, ill-will, and self-advertisement — have 

 found cause to direct themselves against the results of my work. 



To one reproach of a general and impersonal kind I should like to 

 reply here, as it was first raised by one who is now dead, but has been 

 urged again and again by those who wished to bring discredit on my 

 views — the reproach that these views have no stability and that they 

 change so ceaselessly that no one can know what my real opinion is. 

 As a matter of fact, my ideas have changed on many points in the 



