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the enclosing cellulose wall and instead of filling it complete- 
ly withdraws itself in such a way that its outline, near the 
ends, becomes rounded. This change is by no means slow, 
but, when the dimensions of the plant are magnified by the 
microscope, appears to be rapid. I should say, although I 
have not timed it, that this stage occupies from fifteen to 
twenty minutes in its accomplishment. Soon thereafter the 
cell-contents contract still more, moving towards one end of 
the cylindrical cell. Then, with a sudden snap, fracture 
takes place almost entirely across the tough cell-wall at a 
point about one-twelfth of its length from one end, that is 
to say a portion measuring about one-twelfth of the length 
of the whole cell splits across with a perfectly smooth and 
even fracture, still adhering by a very small portion, and 
looking like the lid to a box, is thrown back more or less so 
as to expose the transformed cell-contents to the surrounding 
fluid. Occasionally but not commonly the fracture extends 
entirely across the cell-wall, and the two resulting portions 
become separated. Usually it occurs in the way I have 
described, so that after a while, and when all the cells of a 
filament have thus opened, it becomes transformed into a 
chain of straight portions bent usually in one direction in 
consequence of the dehiscence occurring for the most part 
along one side of the filament only. But now the green 
cell-contents move towards the openings thus formed, and 
slowly and steadily push themselves outwards, and, being 
elastic, escape after the manner that a small elastic sac filled 
with semifiuid contents would escape from the hand if press- 
ure were brought steadily to bear upon it. But in this case 
the emergence is not caused by the closing in of the cell-wall, 
but by a motile power resident in the elastic sac and its 
contents. It is not shot forth suddenly from the cell cavity, 
but squeezes itself out, and as soon as it has escaped assumes 
the form of a perfect sphere, and, as if exhausted by its 
previous exertions, comes to a rest. But, although the 
whole mass is not now in motion, the cell-contents do not 
remain at rest but go on to another change. The bright 
green, coarsely-granular sphere being at rest, is seen first to 
