THE PHENOMENA OF LIFE. 5 



This movement within the pigment cells might also be considered 

 an example of the so-called streaming movement not infrequently 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 streaming granules are seen. A glid- 

 ing movement has also been noticed in certain animal cells; the motile 



Fig. 4. Changes of form of a white corpuscle of newt's blood, sketched at brief intervals. 

 ^The figures show also the intussusception of two small granules. (Schafer.) 



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 the cells of Vallis- 

 neria 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. 5) be viewed under a high magnifying power, streams of proto- 

 plasm containing crowds of granules hurrying along, like the fook 

 passengers in a busy street, are seen flowing steadily in definite direc- 

 tions, 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 

 centre of the cell- cavity. Many of these streams of protoplasm run 



Fig. 5. Cell of Tradescantia drawn at successive intervals of two minutes. The cell-conte <ta 



^usistof a central mass connected by IT ' *" " *^"i fll ***** 



forming a vacuolated mass of protoplasm, 



W 11 ctu .SUl^lJCaoi vo mu^L v t*^ v*. v v ***- ~~ T^Ti iT i 



consist of a central mass connected by many irregular processes to a peripheral film the wlole 



lasm, which is continually changing its shape. (Schofield.) 



together into larger ones and are lost in the central mass, and thut 

 ceaseless variations of form are produced. The movement of the pro- 

 toplasmic granules to or from the periphery is sometimes called vegeta- 

 ble circulation, whereas the movement of the protoplasm round the in- 

 terior of the cell is called rotation. 



The first account of the movement of protoplasm was given by 

 Kosel in 1755, as occurring in a small Proteus, probably a large fresh- 

 water amoeba. His description was followed twenty years later by 



