14 



THE ANIMAL CELL 



fen. 11. 



FIG. 15. Cell of Tradescantia drawn at suc- 

 cessive intervals of two minutes. The cell- 

 contents consist of a central mass connected 

 by many irregular processes to a peripheral 

 film, the whole forming a yacuolated mass 

 of protoplasm, which is continually changing 

 its shape. (Schofield.) 



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 towards or away from the 

 irregular mass in the centre 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 peri- 

 phery is sometimes called vege- 

 table circulation, whereas the 

 movement of the protoplasm round the interior of the cell is called 

 rotation. 



The first account of the movement of protoplasm was given by 

 Eosel in 1755, as occurring in a small 

 Proteus, probably a large freshwater 

 amoeba. His description was followed 

 twenty years later by Corti's demonstra- 

 tion of the rotation of the cell sap in 

 Characese, and in the earlier part of last 

 century by Meyer in Vallisneria, 1827, 

 and by Eobert Brown, 1831, in " Staminal 

 Hairs of Tradescantia." Then came Dii- 

 jardin's description of the granular stream- 

 ing in the pseudopodia of Ehizopods; 

 movements in other animal cells were 

 described somewhat later (Planarian eggs, 

 v. Siebold, 1841 ; colourless blood-cor- 

 puscles, Wharton Jones, 1846). 



There is no doubt that the proto- 

 plasmic movement is essentially the same 

 thing in both animal and vegetable cells. 

 But in vegetable cells the cell-wall obliges 

 the movement to occur in the interior, 

 while in the naked animal cells the move- 

 ment results in an external change of 

 form. 



Although the movements of amoeboid cells may be loosely de- 

 scribed as spontaneous, yet they are produced and increased under 

 the action of external agencies which excite them, and which are 



FIG. 16. Cells from the staminal 

 hairs of Tradescantia. A, fresh 

 in water ; B, the same cell after 

 slight electrical stimulation ; 

 a, ft, region of stimulation ; 

 c, d, clumps and knobs of con- 

 tracted protoplasm. (Kulme.) 



