NATURE OF CELLS 



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are made up of an aggregation of cells, — nucleated masses 

 of protoplasm. In the many-celled animals, the cells are 

 of various shapes and have various functions to perform. 

 Some cells are cyUndrical, some spherical, some flat and 

 scalelike, some like a cube, some like a pyramid, and some 



Pig. 6. — Stages in the division of an amoeba. After Schultze. 



greatly elongated and spindle-shaped. Some cells perform 

 the function of motion, e.g. those of the muscles; others 

 carry impulses, e.g. the nerve cells; others secrete digestive 

 fluids, e.g. those of the salivary glands. To sum up, then, 

 a living animal cell may be defined as a mass of living pro- 

 toplasm with a nucleus and usvally without a definite wall. 



hbkbick's zobi.. — 2 



