Mucus -substance of the Cell in the Characese. 19 



rotation may appear both peculiar and unaccountable ; but that 

 of the sponge-cell, when under progression, particularly in an 

 elongated form, is identical v^-ith it. If we watch the latter, we 

 shall see the granules that are attached to the upper part of the 

 cell move rapidly forwards until they arrive at the advancing 

 boundary, where they sink down, become stationary, and remain 

 there until the rest of the cell has passed over them, when they 

 again ascend from behind, and again are carried on to the an- 

 terior border ; and so on, as the cell progresses, after the manner 

 of a flexible wheel. Thus the mucus-layer in the internode of 

 Nitella rolls round an imaginary oblong axial plane, whose 

 edges correspond with the lines of repose, where, as a matter of 

 course, there is a long linear eddy, in which the mucus is almost 

 stationary, as well as the axial fluid and its particles immediately 

 beneath. 



Were any further proof wanted of the independent contrac- 

 tion or movement of the mucus-layer, that might be cited which 

 I have mentioned when endeavouring to account for the con- 

 tractility of the green layer ; but, in addition to this, I have 

 seen the mucus-layer in an internode of the root of Chara 

 verticillata , when the rotatory movement has been returning 

 after having been arrested, stretch itself directly across the 

 internode, from one part where it had become aggregated into 

 a large mass. The jerking movements which are seen in this 

 mucus after it has been allowed to escape from the internode in 

 the way mentioned, seem to be owing to the successive bursting 

 of the vesicles with which it is filled ; but its diminution in bulk 

 is indicative of something more than common contractility. 

 Lastly, in the cells of the species of Zygnema mentioned, there 

 is not only a ceaseless irritable contractility exhibited in the 

 mucus-layer next the cell- wall, but also throughout the mucus- 

 threads suspending the cytoblast ; and although this motion is 

 not rotatory, which indeed it could hardly be, with the cytoblast 

 so suspended, yet here and there, and particularly against the 

 septa at the extremities of the cell, aggregations of granular 

 mucus, enclosing one or more faint yellow-coloured bodies, like 

 that of the cytoblast, frequently present themselves, which are 

 as unceasingly active in their polymorphism (stretching out 

 their processes here and there) as any portions of Spongilla or 

 Amceba that the eye meets with. 



I have since seen in the youngest, or terminal cell of a filament 

 of introverted Zygnema with single spiral band, a distinct but 

 very irregular travelling up and down of the mucus-layer, 

 exactly like that of the Characese. It can only be seen in the 

 long delicate young cell, where the spiral band is stretched out, 

 and where the minute granules of the mucus are congi-egated to 



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