REGEXERATIOX 



27 



the whole animal, but this can only be because the impelling forces 

 to the regeneration of the whole animal are wanting, that is, that 

 the cut surface only contains the determinants of the tail and not the 

 complete germ-plasm. It might be objected here that the tail-piece 

 is too small to give rise to the whole body, but in Planaria it is 

 onh' very diminutive heads and tails which grow from the artificial 

 incisions, and the same is true of starfshes when only a single arm 

 and a small piece of the disk have been left. Notwithstanding the 

 small amount of living substance at their 

 disposal, and although they are at first un- 

 able to take nourishment, they send out 

 very small new arms (Fig. loi), close up the 

 wounded surface, and, after reconstruction 

 of the mouth and stomach, begin to feed 

 anew. The new arms may then grow to the 

 normal size. 



We must therefore assume that, in many 

 cases, the regeneration-primordium consists of 

 cells which onl}^ contain a definite complex 

 of determinants in the form of latent regenera- 

 tion-idioplasm, as, for instance, certain cells of 

 the tail of Triton contain the determinants 

 of the tail, certain cells of its leg the deter- 

 minants of the leg, and so on. In many 

 cases we can speak even more precisely, and 

 determine from which cells the nerve-centres, 

 from which the muscles, and from which the 

 missing section of the food-canal will he 

 formed, as was recently shown by Franz von 

 Wagner in regard to the worm Lwnilriculus, 

 whose regenerative capacity is so extraordin- 

 arily high. We must then attribute to each of 

 the relevant cells an equipment of regeneration- 

 idioplasm, which includes only the relevant complex of determinants. 



I need not here go further into detail, but I should still like to 

 show that, in reality, as I assumed in regard to the regenerative 

 capacity of a part, the root of the regeneration-idioplasm lies in the 

 germ-plasm, that it is present there as an independent determinant- 

 group, and, like every other bodily rudiment (Anlage), must be 

 handed on from generation to generation. This assumption is 

 necessary, as has been already indicated, on the ground that the 

 faculty of regeneration is hereditary, and hereditarily variable, on 



Fig. ioi. A Starfish arm, 

 growing four new arms ; 

 the so-called 'comet-form.' 

 After Haeckel. 



