GENERAL STRUCTURE OF ANIMALS. 



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Varieties. — This pavement of living cells may be of 

 different patterns; most usually the cells are somewhat 

 rounded (cobble-stone pavement). Sometimes they are 

 flat, polygonal, and fitted together, like a tesselated pave- 

 ment. Sometimes they are elongated and set on end 



Fig. 12. — Different forms of epithelial cells : A, rounded ; B, flat tesselated ; 

 C, columnar ; D, ciliated. 



(columnar epithelium), like wooden block pavements. 

 Sometimes these living cells are provided with cilise, 

 which are in continual waving motion and determine 

 currents on the surface in definite directions (ciliated 

 epithelium) (Fig. 12, A, B, C, D). 



For convenience of reference we give a schedule of 

 the principal kinds and their varieties : 



