Spontaneous movements 21 



In the spirally twisted Arthrospira Jenneri the bending of the entire 

 filaments is more pronounced, and the oscillation of their spiral extremities 

 is more vigorous than in Oscillatoria, although spasmodic and jerky (G. S. W., 

 '04). In Spirulina, in which the filaments are twisted into a very close 

 spiral, there is a well-defined rotation around the axis of the spiral, ac- 

 companied by a decided propulsion of the whole filament. In the species 

 with very long filaments the latter is often a steady and by no means a slow 

 creeping movement. In Spirulina turfosa Bulnh., in which the filaments 

 are relatively short, the rotatory motion is fairly rapid. The hormogones 

 of many of the Hormogonese exhibit slow gliding or creeping movements. 

 It has also been stated both by De Bary ('63) and Phillips ('04) that 

 the filaments of Cylindrospermum are capable of similar movements. All 

 these movements are quicker in bright illumination and at warm tempera- 

 tures than they are in weak light and at cool temperatures. 



The earliest attempts to explain the cause of the movement were by 

 Nageli ('49), who considered it to be due to osmotic currents between 

 the cells and the surrounding water, and Siebold ('49), who regarded it 

 as resulting from an extensive secretion of colourless mucus. Borzi ('86) 

 offered no explanation, but pointed out that isolated cells were incapable 

 of movement, and that no movements were exhibited by any form which 

 possessed heterocysts. Cohn ('67), and also Correns ('96), have stated 

 that the movements could only take place when the filaments were in 

 contact with a substratum, and it is not improbable that in certain species 

 contact with a solid body or with the surface-film of water is actually 

 necessary. Hansgirg ('83) concluded that the movements were due to 

 osmotic currents, and that they only took place within a very thin gela- 

 tinous sheath, which was secreted by the filament and attached to a 

 substratum. Engelman ('79) found the thin mucous secretion described 

 originally by Siebold, but interpreted it as a protoplasmic layer. He attri- 

 buted the creeping movements of the filaments to this secretion, but the 

 oscillating movements he regarded as due to the action of cilia similar to 

 those which occur in the Bacteria. 



The movements are in no way connected with growth, as was suggested 

 by Wolle and others, because all the facts are entirely against such a 

 'conclusion (vide Phillips, '04, p. 316). Nor can a strict comparison be made 

 between these movements and those exhibited by individual diatom-cells. 

 The movements of the latter are now known to be connected with the raphe 

 (vide p. 102), but no such structure exists in the much more primitive cells 

 of the Myxophycea3. Phillips ('04), after carefully reviewing the evidence 

 and adding his own observations, suggests that there are only two plausible 

 explanations of the movements under discussion : either (1) it is effected by 

 a protoplasmic pellicle which creeps along on a substratum and acts in 



