EEGEXERATION 31 



a piece of it the cell -soma is not able to complete itself alone, we have 

 already seen, and the explanation of this fact has always seemed t<j 

 me to be that invisibly minute vital units relating to the regeneration 

 of the injured part leave the nucleus and evoke the development of 

 the missing parts by laws and forces still unknown to us. Loeb has 

 recently claimed that the nucleus is the cell's organ of oxidation : but 

 if that be true it would still not exclude the possibility that the 

 nucleus is also and primarily a storehouse of the material bearers of 

 the primary constituents of a species. It must be regarded as such 

 when we call to mind the phenomena of amphimixis in its twofold 

 aspects as conjugation and as fertilization, and its obvious outcome 

 among higher organisms where it implies the mingling of the 

 parental qualities. 



Thus the ' nuclear substance ' of unicellular organisms is for us 

 the first demonstrable organ of regeneration, and first of all for 

 normal regeneration, which takes place at every reproduction, for 

 instance, of an Infusorian. For we have already seen that, in tlie 

 transverse division of a trumpet animalcule (Sterdor), the anterior 

 part must develop the posterior half anew, while the posterior half 

 must develop the much more complex anterior half, Avith mouth 

 region and spiral bands of cilia. But as soon as the arrangement for 

 normal reproduction was elaborated, as soon as the nucleus was 

 present, as a depot of ' primary constituents,' this implied the pos- 

 sibility of regeneration in exceptional cases, that is, after injury. 

 The mechanism was already there, and it came into operation as soon 

 as a part of the animal was missing. 



It is in the first nucleus, therefore, that we have to look for the 

 source of all regenerative capacity, both in unicellular and multi- 

 cellular organisms. But with the origin of the latter a limitation 

 took place, either quite at the beginning or a little later, for each 

 nucleus of the cell-colony no longer contained the whole complex of 

 ' primary constituents ' or determinants of the species, but, in many 

 cases, onl}^ the reproductive cell possessed them. As soon as this began 

 to develop into a whole by cell-division the determinant-complex was 

 segregated. Thus the first cell-colonies with two kinds of cells arose, 

 as we have seen in the care of Volvox — the reproductive cells with 

 a complete equipment for regeneration in their nucleus, and the 

 somatic cells with a limited equipment for regeneration in their 

 nuclei. The somatic cell could no longer give rise anew to the whole 

 organism, but could only reproduce itself or its like. 



But as many of the lower Metazoa and Metaphyta possess the 

 poiver of Imdding, that is, are able not only to produce a new indi- 



