"SLIDING MOVEMENT"— ITS CAUSE 321 



be distinctly demonstrated by the stability of its reticular 

 and radiating structures, it follows that the granules must 

 possess a movement of their own, and that it is impossible 

 to suppose that they are being carried along by streams of 

 the protoplasm. 



This conception of granular movement is not so new as it 

 might appear from the widespread belief in the contrary view. 

 Nageli at any rate has described, as far back as 1855, a 

 granular movement quite corresponding to that here 

 described on the inner surface of the primordial utricle of 

 DesmidiaceoB (Glosterium in particular) ; he has termed it 

 " sliding movement " (Glitsclibewegung). The movement 

 also of the granules on the inner surface of the protoplasm 

 in AcMya, where the cell sap is traversed • by protoplasmic 

 filaments, as frequently occurs also in Surirella, is regarded 

 by Nageli in just the same manner. This so-called sliding 

 movement has later been comprised as a subordinate case of 

 general protoplasmic movement (so also Berthold, 1886, for 

 instance), in which the streaming movements of the proto- 

 plasm are very feeble and irregular. Since, at an earlier date, 

 when protoplasmic structures had not been accuratelj'^ traced, 

 it was impossible to decide with certainty whether the move- 

 ment of the granules was caused by the general streaming 

 movements of the protoplasm or not, there was much to be 

 said for the view, which subordinated the particular case to 

 the more general phenomenon. Since, however, we are now 

 able to convince ourselves, as has been said, that the proto- 

 plasm as such does not take any share in the movements of 

 the granules in Surirella by means of any noticeable stream- 

 ing movements or displacements, this explanation falls to the 

 ground. On the ground of his observations upon the so- 

 called sliding movements, Nageli, and with him Schwen- 

 dener (1865), held fast to the view that the protoplasmic 

 granules must also possess an automatic power of movement 

 in circulation and rotation, and that the seat of the motor 

 forces was to be looked for in the granules themselves. 

 Originally, in 1855, Nageli thought of hydro-electric forces, 

 but later (1865) he preferred to assume that the so-called 

 sliding movements, and hence, of course, the cause of the 



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