SPECIALISATION OF CELLS 95 



purposes of digestion of the food of the whole organism. 

 Some of the gland cells lining the air passages are 

 ciliated and others produce mucus (Fig. 5, B), 



Fig. 5. — Cells from difierent tissues of a higher vertebrate animal. 

 A, blood corpuscles ; r, red corpuscles — these are not complete 

 cells and have no nuclei ; w, white corpuscle, whose structure 

 and movements are very similar to those of amceba. B, cells 

 of the ciliated glandular epithelium lining the trachea (air tube 

 to lungs) ; n, nucleus ; m, mucus being expelled from the cell ; 

 c, cilia. C, cells of cartilage recently divided, embedded in 

 cartilaginous matrix secreted by the cells; n, nucleus. D, cells 

 and fibres of connective tissue (which forms the " packing " of the 

 organs of the body) ; n, nucleus. E, fat-forming cells ; /, globules 

 of fat; n, nucleus, F, Part of striped muscle fibre. Here the 

 protoplasm is highly modified into special contractile substance ; 

 n, nucleus : many nuclei in each fibre, which is composed of many 

 fused cells. The nuclei are situated just below the very thin 

 outer membrane. 



