EPITHELIUM. 



25 



The cell-substance is often modified in its chemical nature ; its external 

 layer may become hardened to form a sort of menfbrane, or the whole 

 cell may become horny (keratinised) ; or the cell may develop fibrils 

 within it, and passing from it into adjacent cells, or lastly, there may 

 be an accumulation of materials within the cell which are ultimately 

 either used by the organism, as in the ordinary secreting glands, or 

 eliminated as waste products as in the kidney. 



FIG. 22. EPITHELIUM-CELLS OF SALAMANDEK LARVA IN DIFFERENT PHASES OF. 

 DIVISION BY KARYOKINESIS. (Flemming.) 



Division of the cells. The division of a cell is preceded by the 

 division of its attraction-sphere, and this again appears to determine 

 the division of the nucleus. The latter, in dividing, passes through a 

 series of remarkable changes (fig. 22), which may thus be briefly 

 summarised : 



1. The network of chromoplasm-filaments of the resting nucleus 



