THE CELL 19 



nuclear substances are the chromatin and the linin, the 

 former having a marked affinity for all nuclear stains, 

 while the latter remains unaffected. These chromatin- 

 bodies are explained more fully in the chapter on cell- 

 division. 



The majority of cells contain a single nucleus, some 

 of the protozoa are supplied with two, while other forms 

 apparently contain a large number of nuclei lying in an 



N, the Nucleolus ; <7A, chromatin network ; NM, nuclear 

 membrane ; C, the centrosome ; F, vacuole. 



undifferentiated mass of protoplasm. These latter are, 

 however, in many cases not a single cell in the usual 

 sense, but a body formed by the coalescence of a number 

 of cells. 



The shape of the nucleus may vary exceedingly. It 

 may be spherical, ovoid, branched, horse-shoe shaped, 

 reticular or even monilifonn. 



The cell wall also is subject to considerable variation. 

 In most of the lowest forms of life there is none, and this 

 is also true of the greater number of cells in the metazoa. 

 From this stage, with no cell wall but only a slightly 



