The Cellular Basis 199 



Actual observation shows that by the interaction with one 

 another of substances or parts originally present and by their 

 reactions to external stimuli new substances and parts appear 

 which had no previous existence just as new substances result 

 from chemical reactions. This is "creative synthesis" in general 

 science, epigenesis in development. Differentiations appear 

 chiefly in the cytoplasm but only as the result of interaction be- 

 tween cytoplasm and nucleus. Similarly, it may be argued, smal- 

 ler units of organization such as chromosomes or chromomeres 

 do not in themselves give rise to any adult parts, but only as they 

 interact upon other units are new parts formed. 



In many cases the first formation of such new substances ap- 

 pears in the immediate vicinity of the nucleus and, like assimila- 

 tion itself, this is evidently brought about by the interaction of nu- 

 cleus and cytoplasm. In certain cases it can be seen that the 

 achromatin and oxychromatin which escape from the nucleus 

 during division take part in the formation of new substances in 

 the cell body, and since the oxychromatin is derived from the 

 chromosomes of the previous cell division, it is probable that the 

 chromosomes are a factor in this process. 



Weismann maintained that the chromosomes and the inheri- 

 tance units contained in them undergo differentiation by a pro- 

 cess of disintegration and that these disintegrated units escape 

 into the cell body and there produce different kinds of cytoplasm 

 in different cells. A somewhat similar view was advanced by 

 deVries in his theory of "intra-cellular pangenesis." However, as 

 we have seen already, there is good evidence that the chromosomes 

 do not undergo progressive differentiation in the course of devel- 

 opment; they always divide with exact equality, and even in 

 highly differentiated tissue cells their number and form usually 

 remain as in embryonic cells. 



On the other hand the cytoplasm undergoes progressive dif- 

 ferentiation, and when by pressure or centrifugal force it is 

 brought into relations with other nuclei the differentiations of 

 the cytoplasm are not altered thereby, thus showing that the dif- 



