188 HEREDITY AND ENVIRONMENT 



itself, is evidently brought about by the inter- 

 action of nucleus 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 chromo- 

 somes of the previous cell division, it is prob- 

 able that the chromosomes are a factor in this 

 process. 



Weismann maintained that the chromo- 

 somes and the inheritance units contained in 

 them undergo differentiation by a process of 

 disintegration and that these disintegrated 

 units escape into the cell body and there pro- 

 duce different kinds of cytoplasm in different 

 cells. A, somewhat similar view was advanced 

 by deVries in his theory of intra-cellular pan- 

 genesis. However, as we have seen already, 

 there is good evidence that the chromosomes 

 do not undergo progressive differentiation in 

 the course of development; they always divide 

 with exact equality, and even in highly differ- 

 entiated tissue cells their number and form 

 usually remain as in embryonic cells. 



