132 THE GERM-PLASM 



that is, regeneration in two directions — cannot take place in the 

 higher animals. 



If, then, regeneration depends on the distribution of supple- 

 mentary determinants to certain cells, which occurs whenever it 

 is necessary or possible, the process must be primarily traceable 

 in the case of the Metazoa to the doubling of the ids in a certain 

 ontogenetic stage. And since a division and doubling of the 

 idants takes place in every mitotic nuclear division, this hypothesis 

 is supported by actual fact, even although we are still far from 

 being acquainted even with the general details of the processes 

 of growth and doubling of the ids and determinants, not to 

 mention the systematic transference of such inactive determi- 

 nants to definite cells and series of cells. Here again, however. 

 Nature will have caused an advance from the simple to the more 

 complex ; and it therefore follows that, just as complicated 

 organisms could only arise in the course of innumerable series 

 of generations and species, so also the complex apparatus for 

 regeneration in the tail or limb of a newt could not have been 

 developed suddenly, but must have arisen in consequence of 

 similar modifications in innumerable ancestors. 



It might be possible to picture to one's self approximately the 

 series of modifications which the apparatus for regeneration has 

 gradually undergone, beginning at the lowest multicellular 

 forms, and passing upwards to those animals in which the power 

 of regeneration is the most highly developed and complex. I 

 shall not, however, attempt to do so. At some future date it 

 may perhaps be found that differences occur as regards the 

 number of ids contained in the cells of those which have, and in 

 those w'hich have not, a marked capacity for regeneration : it 

 will not be worth while to trace in detail the courses which the 

 development of the power of regeneration has taken, until our 

 knowledge of the idioplasm is sufficiently complete to furnish a 

 basis for the theory in fact. 



4. Regeneration in Plants 



The process which may be described as regeneration in the 

 case of the lower plants — the algae, fungi, and mosses — will be 

 treated of in greater detail subsequently. In this place, I merely 

 wish to point out that true regeneration only occurs in a very 

 slight degree in all the higher plants which are regarded as 



