CH. II.] 



PROTOPLASMIC MOVEMENT 



13 



were, drawn into it. The Amoeba thus comes to occupy a new 

 position, and when this is repeated several times we have locomotion 

 in a definite direction, together with a continual change of form. 

 These movements, when observed in other 

 cells, such as the colourless blood-cor- 

 puscles of higher animals (fig. 13), in the 

 branched corneal cells of the frog and 

 elsewhere, are hence termed ' amoeboid. 

 The projections which are alternately 

 protruded and retracted are called pseudo- 

 podia. FlG . 12. Amcebse. 



A streaming movement is not infre- 

 quently seen in certain of the protozoa, in which the mass of 

 protoplasm extends long and fine processes, themselves very little 

 movable, but upon the surface of which freely-moving or stream- 

 ing granules are seen. A gliding movement has also been noticed 



FIG. 13. Human colourless blood-corpuscle, showing its successive changes of outline within ten 

 minutes when kept moist on a warm stage. (Schofleld.) 



in certain animal cells ; the motile part of the cell is composed of 

 protoplasm bounding a central and more compact mass ; by means 

 of the free movement of this layer, the cell may be observed to 

 move along. 



In vegetable cells the protoplasmic movement can be well seen 



FIG. 14. (A.) Young vegetable cells, showing cell-cavity entirely filled with granular protoplasm 



enclosing a large oval nucleus, with one or more nucleoli. 



(B.) Older cells from same plant, showing distinct cellulose-wall and vacuolation of proto- 

 plasm. 



in the hairs of the stinging-nettle and Tradescantia and the cells of 

 Vallisneria and Chara ; it is marked by the movement of the granules 

 nearly always imbedded in it. For example, if part of a hair of 

 Tradescantia (fig. 15) be viewed under a high magnifying power, 



