36 MOVEMENTS OF PROTOPLASM IN CELL-CAVITIES. 



"swarming." It is difficult to imagine the kind of motion possessed by the 

 protoplasm in which these swarming microsomata are embedded; but however 

 closely it is confined, there must be continual rapid displacements in its substance, 

 which is very fluid, and it may be assumed that here again it is not so much 

 the tiny grains that bestir themselves as the protoplasm which holds them. 

 Probably the protoplasmic matter spreads and stretches out and rotates, and 

 individual granules are carried about by it. This, of course, does not exclude 

 the possibility of the granules possessing a vibratory motion of their own within 

 the mass of protoplasm. 



Similar, but not identical, is the swarming movement of protoplasm observed 

 in cells of the Water-net (Hydrodictyon utriculatuTn), and in several other plants 

 allied to it. Hydrodictyon looks like a net in the form of a sac, and composed 

 of green threads. The meshes of this net, which are generally hexagonal, consist, 

 however, not of filaments but of slender cylindrical cells joined together by threes 

 at their extremities, somewhat in the same way as are the leaden frames of the 

 little hexagonal panes of glass in gothic windows. The protoplasmic body of 

 one of these cells in due time breaks up into a great multitude (7000-20,000) of 

 tiny clots, which begin to move and swarm within the cell-cavity in what appears 

 to be a disordered medley. In half an hour, however, the excited mass is again 

 restored to rest: the minute particles take form and arrange themselves in definite 

 order, each having two others at either extremity, making an angle of 120° with 

 it; and, lastly, all unite to form a single tiny net having exactly the same shape 

 as the one whose component cell constituted the arena of this process of construc- 

 tion. The miniature water-net so formed then slips out of the cell, the latter 

 opening for the purpose, and in from three to four weeks it grows to the same 

 size as the parent plant. 



In the above we have an instance of a protoplast producing a whole colony 

 of cells, which are obliged to leave their home for want of space. In cases 

 previously considered we have found the protoplast stretching and elongating 

 in all directions, drawing itself out into bridles and spreading as a delicate lining 

 to walls, and so endeavouring generally to expand and present the greatest surface 

 possible. Again, we have seen it wandering freely, creeping, swim.ming, and 

 rotating, and by this method also covering as much space as it can. But, con- 

 versely, there is a time when a protoplast tends to the other extreme; the 

 expanded mass of its body gathers itself together again, contracts more and 

 more, and at length becomes a resting sphere, that is to say, it assumes the con- 

 figuration which exposes the least surface to the environment. 



This process exhibits itself with particular clearness within the cell-cavities 

 of the green algas known by the name of Spirogyra, a species of which is 

 represented, magnified three hundred times, in figure 25a, I. In this alga 

 the protoplasm in each mature cell-cavity forms, as a general rule, a very deli- 

 cate parietal lining wherein green chlorophyll bodies are embedded, arranged 

 in a spiral band. All of a sudden, however, this lining strips itself ofi" the inner 



