52 



THE ELEMENTS OF STRUCTURE 



(b) A Specialised nucleus, with a complex structure, 

 and important functions ; 



(c) One or more specialised bodies called central 

 corpuscles or centrosomes, which seem to be centres of 

 activity during cell division ; 



{d) A cell wall, which occurs in very varied form, or may 

 be entirely absent. 



(a) As to the cell substance, it appears in living cells to be 



Fig. 25. — Diagram of cell structure. 

 — After Wilson. 



PL., Plastids in cytoplasm ; CC, centrosomes in 

 centrosphere ; n., nucleolus ; N., nucleus ; 

 CHR., chromosomes ; CT., general cytoplasm ; 

 v., vacuole ; GR., granules. 



clear, colourless, structureless, and more or less fluid. 

 There are great variations in viscosity from cell to cell, 

 from time to time, and even from place to place within a 

 single cell at one instant. In cells " fixed " and prepared 

 for microscopic study the cytoplasm has an artificial 

 reticular or fibrillar structure. 



The cytoplasm often contains numerous inclusions. 

 Granules, watery droplets or vacuoles, and oily globules 

 are present in varying numbers ; they are regarded as non- 



