REGENERATION 



109 



be easily conceived by supposing an aggregation and redistribu- 

 tion of the determinants to occur in the idioplasm, the process 

 of idic division becomes very complicated when the primarv 

 and secondary development take place along different lines : 

 for in the latter process the combinations of supplementary 

 determinants in the id of the cell-generations must be different 

 from those which occur in the former. But this difference is 

 evidently due merely to a greater complication of the process, 

 and it does not stand in the way of the theory. In all cases of 

 regeneration, the mode in which the supplementary determi- 

 nants become split off must be previously arranged for in the id. 

 The assumption of a mere increase in the power of multiplica- 

 tion of certain determinants might seem sufficient in the case 

 of palingenetic regeneration, for this would lead to one portion 

 of a certain group of determinants becoming separated off as 

 accessory idioplasm at a particular ontogenetic stage. In 

 coenogenetic regeneration, however, we can only assume that a 

 double or still greater number of determinants are present in the 

 germ-plasm, one set of which are destined for embryonic devel- 

 opment and the others for regeneration ; and these are previ- 

 ously arranged with reference to their internal forces, particularlv 

 that of multiplication, so that at a certain stage of development 

 they become split off as • accessory idioplasm.' either alone or 

 together with the adjacent -regenerative determinants.' 



It seems to me, however, that palingenetic regeneration 

 cannot be satisfactorily accounted for unless we assume the 

 existence of special regenerative determinants, for it would 

 otherwise be impossible to explain the phyletic origin of the 

 ccenogenetic variations in the process of regeneration. These 

 latter must, indeed, depend on variations in a determinant of 

 the germ-plasm. If however the latter contained only the one 

 determinant destined for embryogeny. variations must occur in 

 the latter process at the same time. But this is not the case, 

 and consequently a kind of double determinant must be con- 

 tained in the germ for those hereditary parts (determinants) 

 which are capable of becoming regenerated : — that is to say, two 

 originally identical determinants must be present, one of which 

 becomes functional in embrvogenv and the other in reo-enera- 

 tion. This will be made apparent if we take some examples. 



In most existing amphibians the caudal region of the vertebral 

 column may undergo regeneration, although its embryonic 



