MOVEMENTS OF SIMPLE ORGANISMS. 39 
the dust, which are dissolved in the melted snow. They grow and at last divide 
so as to form daughter-cells, usually four in number but often six or eight and 
less frequently two only (Pl. L, fig. f, g). As soon as the division is accom- 
plished, the daughter-cells, so produced, free themselves, assume an oval shape, and 
display at their narrower extremity two rotating eilia by means of which they 
move about in snow-water with considerable vivacity. The interstices of the still 
unmelted, but now granular, snow, are filled with water from the melted parts, and 
through these the red cells swim away and are thus diffused over the snow-field. 
At the moment of escape and first assumption of movement the cell-body appears 
to be uninclosed. But it soon clothes itself with an extremely delicate, though 
clearly discernible skin, which, curiously enough, does not lie close to the proto- 
plasm, which is withdrawn slightly and inclosed as in a distended sae (see 
Pl. I. fig. e). Only in front, where the two cilia carry on their whirling motion, 
does the skin lie close to the body of the cell; and it must be presumed that the 
cilia, which are simply extensions of the protoplasmic substance, are projected 
through the envelope. The swarm-spores afford an example of an unusual type of 
protoplasts, namely of those that move about singly in the water by means of cilia 
and at the same time carry their self-made cell-membranes with them. 
How long the motile stage lasts under natural conditions has not been deter- 
mined for certain. On the mountains of central and southern Europe, where hot 
days are followed, even in the height of summer, by bitterly cold nights, causing 
the melted snow which has not run off to freeze again in the depressions of the 
snow, the movement no doubt is often interrupted. On the other hand, in high 
latitudes, where the summer sun does not set for weeks together, such interruption 
would be exceptional. In any case, however, the locomotion of the red cells with 
their hyaline cell-membranes is not limited to so short a period as is that of naked 
ciliated protoplasts. Moreover they have the power of nutrition and growth like 
the red resting-cells from which they originate, and they have been observed, in a 
culture, to increase in size fourfold within two days. When at last they come to 
rest they draw in their cilia, assume a spherical shape, thicken their cell-membrane, 
which now once more lies close to the protoplasmic body, and divide anew into two, 
four, or eight cells (Pl. I., fig. f, g). The fusion of the protoplasts of the red cells in 
pairs, and their sexual propagation, which has been observed in addition to the 
above-described asexual multiplication, will be the subject of discussion later on. 
At present we need only add with reference to this remarkable plant that it was 
named Spherella nivalis by the botanist Sommerfelt, and that not only in mode 
of life, but also in form and colour, it most closely resembles a kind of blood-red alga, 
which makes its appearance in Central Europe in little hollows temporarily filled 
with rain-water in flat rocks and slabs of stone, and also inside receptacles exposed 
to the open. This alga has received the name of Spherella plwvialis, and also 
that of Hamatococcus pluvialis. 
Lastly, we have to consider the mysterious movements exhibited by many 
Diatomacex, and by the filamentous species of Zonotrichia, Oscillaria, and 
