THE ANIMAL CELL. 



21 



Animal cells as a rule are not provided with such well de- 

 veloped and resistant walls as are plant cells. 



38. Cell Functions. Since the cell is only a definite mass 

 of protoplasm, its functions are in general those which have 

 already been described as protoplasmic functions. They are 

 merely localized within the cell. The cell wall when pres- 

 ent would naturally modify and limit in important ways, 

 the more active protoplasmic functions. In such cases the 

 independent motion characteristic of so many cells must be 

 accomplished by special devices. These frequently take the 

 form of cilia or flagella, which are thin protoplasmic projec- 

 tions used after the manner of oars. Locomotion of cells 

 is not confined to single-celled organisms, but is found in 

 many cells of the higher animals and plants as colorless 



FIG. 5. 



C 



m. 



FIG. 5. Modes of cell reproduction. A, B, and C, stages in the reproduction of the 

 Infusorian, Colpoda, by the breaking up of the protoplasm to form numerous cells. 

 A, encysted stage; B, protoplasm escaping, spores partly formed; C, spores com- 

 pletely separated (adapted from Rhumbler) ; D, budding in Chlamydomyxa, a lowly 

 Rhizopod. b, bud; cw., cell wall; m, mother cell; n, nuclear matter; s, spores. 



Questions on the figure. Compare the process and the results of the 

 two modes of cell reproduction shown in this figure. Can you describe the 

 fate of the " mother " cell in the two cases ? 



