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POPULAR SCIENCE REVIEW. 
Fig. 5. 
the phenomenon is presented by an abundant and well-known 
fresh-water Alga, Spirogyra longata , which forms a most 
beautiful object under the microscope, from its chlorophyll- 
grains being combined in each cell into a spiral band visible 
through the transparent cell-wall. Figs. 3, 4 represent the 
mode in which this process takes 
place. The filaments of this Alga 
consist of a row of cylindrical cells, 
each of which contains a mass of 
protoplasm, and the conjugation takes 
place between the adjacent cells of 
two more or less parallel filaments. 
Protuberances (fig. 3 a) first of all 
make their appearance at opposite 
points of these adjacent cells, which at 
length meet (6). The cell-wall then 
gives way between them (fig. 4 a), 
and the two masses of protoplasm 
coalesce, the whole finally passingover 
into one of the cells (6), andthe result- 
ing mass at length becomes coated with 
a cell-wall of cellulose (c), forming 
the reproductive body known as a 
u Zygospore.” In the unicellular 
Desmids and Diatoms, and in the 
Mucorini, the process is similar. 
3. Renewal or Rejuvenescence of 
Cells . — This process takes place in 
the formation of the “ Swarmspores ” 
or “ Zoospores ” of Algae. The whole 
contents of a cell of a filament con- 
tract, and the mass of protoplasm as- 
sumes an ovoid form, with a broad 
green and a narrower hyaline end, 
provided with cilia or fine threads 
of protoplasm either at this latter 
end or surrounding the whole spore. 
The cell-wall gives way, and, as the 
swarmspore escapes from it, it moves 
rapidly forward with its narrower 
end in front, propelled by the vibratile motion of its cilia, till it 
at length comes to rest, when its cilia disappear, and it 
attaches itself by means of rhizoids or root-hairs ; and then only 
the naked ball of protoplasm becomes coated or encysted with 
a cell- wall secreted out of its own substance, and finally de- 
velopes into a new filamentous Alga. Fig. 5 shows the various 
stages of this process in the case of an (Edogonium . This 
A-D, various stages in the de- 
velopment of the swarm- spore 
of an (Edogonium from the 
protoplasm of a cell ; E, escape 
of the whole of the protoplasm 
from the single cell of a young 
(Edogonium. (After Prings- 
heim, x 350.) 
