4 THE PHENOMENA OF LIFE 



several times we have locomotion in a definite direction, together with a con- 

 tinual change of form. These movements, figures 3 and 4, are observed in 

 such cells as the colorless blood corpuscles of higher animals, in the branched 

 corneal cells of the frog and elsewhere, and are termed ameboid. 



The remarkable movement of pigment granules observed in the branched 

 pigment cells of the frog's skin by Lister are also probably due to ameboid 

 movement. These granules are seen at one time distributed uniformly 

 through the body and branched processes of the cell, while at another time 

 they collect in the central mass leaving the branches quite colorless. 



This movement within the pigment cells might also be considered an ex- 

 ample of the so-called streaming movement not infrequently seen in certain 

 of the protozoa, in which the mass of protoplasm extends long and fine proc- 

 esses, themselves very little movable, but upon the surface of which freely 



6. 



FiG. 4. Changes of Form of a White Corpuscle, Sketched at Brief Intervals. The figures 

 show also the ingestion of two small granules. (Schafer.) 



moving or streaming granules are seen. A gliding movement has also been 

 noticed in certain animal cells; the motile part of the cell being 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 in the 

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

 and Chara; it is marked by the movement of the granules nearly always em- 

 bedded in it. For example, if part of a hair of Tradescantia, figures 5 and 6, 

 be viewed under a high magnifying power, streams of protoplasm containing 

 crowds of granules hurrying along, like the foot passengers in a busy street, 

 are seen flowing steadily in definite directions, some coursing round the film 

 which lines the interior of the cell wall, and others flowing toward or away 

 from the irregular mass in the center of the cell cavity. Many of these streams 

 of protoplasm run together into larger ones and are lost in the central mass, 

 and thus ceaseless variations of form are produced. The movement of 

 the protoplasmic granules to or from the periphery is sometimes called 



