THE BIOLOGY OF THE CELL SURFACE 



sperm-producing areas as motile swimming organisms 

 arise, restriction has taken place by removal of these free 

 potencies. 



8. Regeneration of lost parts is encountered in all ani- 

 mals; In some, as the flatworms, it reaches the level of 

 asexual reproduction; in others, capacity for regeneration 

 is limited. In some forms regeneration is said to be due 

 to the presence of formative cells, cells in which it is assumed 

 that differentiation has been arrested; in others regenera- 

 tion of structures occurs from tissues that normally never 

 give rise to them.^ In either case the capacity for regenera- 

 tion may be thought of as a reorganization under the influ- 

 ence of the liberation of potencies, previously bound by 

 the chromosomes, into the cytoplasm induced by the 

 changed condition of the cells as a result of the injury or 

 loss. 



9. Abnormal growths or tumors can be explained in the 

 same way. Some change In the environment of the cells 

 stimulates the throwing out by the nuclei of potencies into 

 the cytoplasm where a new type of development is set up. 

 A tumor-cell is one which has escaped the domination exer- 

 cised by contiguous cells. It becomes physiologically 

 isolated. 



In view of all of these facts that support my theory of 

 differentiation as genetic restriction, I state this again: 

 As development progresses, the egg-potencies are restricted 

 through their withdrawal from the cytoplasm by the 

 chromosomes with each successive cell-division. Thus the 

 cytoplasm forms functional areas. At some time in the 

 history of the egg's development the potencies, having 

 been previously taken out and stored by the chromosomes 

 during cleavage and succeeding stages of differentiation, 

 escape into the cytoplasm. The cytoplasm of the fertilized 

 or parthenogenetlcally developing t^g restores them again 



' Reed, 1904. 



■ 320 



