MOTION AND LOCOMOTION 43 



living, is in constant motion, and it consists in a regular 

 movement of the cytoplasm within the limits of the 

 cell ; and it is possible that it subserves two purposes, 

 namely, of bringing every portion of the cytoplasm into 

 contact with the food, and of enabling all the food to 

 be acted upon by the enzymes contained in the cell. 

 This type of movement is seen to special advantage in 

 plant cells, such as the cells of Elodea and the hairs of 

 Tradescantia. 



A slight step in advance is seen in certain of the 

 unicellular organisms, for example, 

 amoeba, where there is in addition 

 to the circulation of the proto- 

 plasm a primitive type of loco- 

 motion which we call amoeboid 

 movement. This movement con- 

 sists in a flowing of the protoplasm 

 which may be compared to rolling, 

 and causes distension of the ceU Cell showing Circulation 

 outlines and results in a slow of Protoplasm, 

 progress. This type of movement is not confined to 

 amoeba ; it is found in the leucocytes of the blood 

 and in gland cells, &c., and in the plant world we see 

 it in the Slime Fungi, and in the reproductive cells of 

 many Fungi and Algae. In addition to this amoeboid 

 type of movement, two other types, ciliary and flagellar, 

 are exhibited by numerous of the lower forms of both 

 plants and animals. In the higher animals ciliary 

 movement, which is due to the action of minute hair- 

 like outgrowths, is seen in the cells lining many of the 

 tubes in the body, and in the cells covering the gills of 

 mussels ; while flagellar movement, due to longer, more 



