THE BIOLOGY OF THE CELL SURFACE 



the discussion involving better known structures. The 

 changes in the hyaHne plasma-layer are therefore taken up 

 beyond, after its structure has been elucidated. 



The foregoing description of the changes in nucleus, 

 centrospheres and astral radiations agrees with the accounts 

 given by others for the eggs of several species of sea-urchins. 

 According to all of these the centrospheres and astral rays 

 steadily increase in size until the stage of the telophase 

 whereupon they begin to decrease; later, cleavage occurs. 

 That is, cleavage does not take place when centrospheres 

 and astral rays are at their maximum size. In spite of this 

 mass of well established observations, theories of the 

 division of the cell-body have been fabricated upon the 

 false idea of a coincidence of cell-division with the maximum 

 size of the aster. ^ I do not see any necessity to discuss 

 such theories. 



As stated above, this chapter, whilst it deals with cell- 

 division primarily in eggs, has to do with the process in its 

 widest aspects. Thus we are here concerned with all forms 

 of division of the protoplasmic mass. It is to the phenome- 

 non as one widely occurring in all living cells that I wish 

 now to direct attention. I raise the question: Do the phe- 

 nomena observed in the division-process of sea-urchins' 

 eggs possess general significance for the problem of cell- 

 division : In order to answer this question we must estab- 

 lish those features in the division of the sea-urchins' eggs 

 which have their parallel in the division both of eggs of 

 other species and of other cells, and must eliminate whatever 

 is peculiar to this egg only. 



There are other eggs that like the sea-urchins' show that 

 form of mitotic division of the nucleus in which centro- 

 spheres and asters are present. But whilst the centro- 

 spheres of the first clea\'age-figure of eggs of sea-urchins 



^ Chambers^ 192^; Gray, 1931. 



26^ 



