16 E. J. LUND 



Bradley ('15) on the autolysis of liver cells, such a controlling 

 factor seems to be the hydrogen ion concentration. 



I am unable to conceive how from the standpoint of physical 

 or chemical phenomena a 'making over/ 'regulation/ 'reorgani- 

 zation/ 're constitution/ 'rejuvenation' of a differentiated part 

 of a cell can be accomplished so as to supply missing parts of a 

 different structure unless the differentiated parts which remain 

 are first broken down or simplified, at least to some extent, and 

 then rebuilt to form the normal structure. Furthermore evi- 

 dence points to the conclusion that mechanisms for such break- 

 down of cell structure are of wide occurrence in many cells. 4 



VIII. RELATION OF MORPHOGENETIC PROCESSES TO HEREDITARY 

 CONSTITUTION OF BURSARIA 



If we should assume that the determiners for the structures in 

 Bursaria were 'located' in the nuclear mechanism we would 

 have to consider the parts played by the macronucleus and the 

 micronuclei. So far as the macronucleus is concerned we have 

 seen that regulation leads to the same result whether a big or a 

 small piece of the macronucleus is present; evidently any part 

 of the macronucleus is equivalent to every other part so far as 

 regeneration of the missing structures is concerned. If the 

 macronucleus contains the determiners for the cell characters 

 evidently there must be many like determiners for the same 

 character, distributed throughout the macronucleus. It is im- 

 possible to apply a similar analysis to the micronuclei, for in 

 Bursaria there are from 9 to 15 or more micronuclei and some of 

 these are probably always included in a piece. So far as I am 

 aware Calkins ('11, page 104) is the only investigator who has 



4 To make the idea clearer by using a crude illustration: if half of a masonry 

 house having a definite architectural design (differentiation), was removed, and 

 it was required to make a house out of the remaining half, of the same archi- 

 tectural design as the original, then the simplest and only possible way would 

 be to tear it down and rebuild a smaller one out of the stones that remained 

 in the part of the old house. The process of rebuilding (redifferentiation) would 

 be conditioned by the isolation of the stones of the remaining structure (de- 

 differentiation) which now would be available for recombination to form a new 

 structure of the same architectural design but half the size of the original one. 



