MOVEMENTS OF PROTOPLASM IN CELL-CAVITIES. 35 
study it is apparent that the granules which seem to be travelling on the proto- 
plasmic thread are covered by a delicate and transparent protoplasmic pelliele. 
Thus, these granules imbedded in the substance of protoplasts have no independent 
motion, but are pushed along by the spreading protoplasm. 
Each stream of protoplasm is shut off from its environment and limited by 
a layer tougher than the rest. But this does not prevent the currents, with their 
crowds of drifting granules, from changing their direction. In fact we have 
only to follow for a short time the course of one such granular stream to remark 
a continuous series of changes: a current from being in a straight line bends 
suddenly to one side, it broadens and contracts again, now it runs close alongside 
another channel, now breaks away once more, divides into two little arms, and 
loses itself finally in the primordial utricle. On the other hand, fresh folds start 
from the primordial utricle, stretch and grow until they have pushed across the 
cell-cavity to the other side in the form of bands, or the protoplasm may be 
drawn out into threads, which elongate until they encounter other similar strings 
and form a junction with them. The same processes then that are observed in 
free creeping protoplasts take place to some extent here. Imagine a protoplast 
captured whilst on its travels—creeping along the level ground—and imprisoned 
in a completely closed vessel; it would spread itself out over the inner surface 
of the vessel, would branch and creep about and have just the same appearance 
as the protoplasts, just described, which inhabit cell-cavities from their earliest 
youth. This is but the converse of the power possessed by a protoplast set free 
from its cell, which enables it to move, stretch out, and draw in its various parts, 
and so to effect locomotion. 
Another motion, differing from the creeping, gliding, and streaming action 
of protoplasts, manifests itself in the so-called swarming of granules contained 
in the protoplasm. It may be best observed in the cells of the genera Peniwm 
and Closteriwm, both of which are shown in Plate I, figs. ©, k, though 
the same phenomenon is to be seen in many allied forms, living in lakes and 
ponds either singly or congregated in colonies, and remarkable for their bright 
green colour. The above-mentioned genus Closteriwm includes delicate unicellular 
forms having a curved or scimitar shape unusual in plants, whence one of its 
species, in which the semi-lunar form is most striking, has been named Closterium 
lunula. The cell-membrane in all these little water-plants is clear and quite 
transparent. The greater part of the cell-contents consists of a dark-green 
chlorophyll body longitudinally grooved; but the protoplasm which is visible in 
the two sharply tapering ends of the cell-cavity is colourless, and embedded 
within it is a swarm of microsomata. These granules or microsomata appear to 
be in a most curious state of motion so long as the protoplast lives. They are 
to be seen plainly within the limits of the tiny cavity, jumping up and down, 
whirling, dancing, and rushing about without really changing their position. One 
is reminded of the apparently purposeless journeyings to and fro within reach 
of their homes of ants or bees, and the movement has been called not inaptly 
