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POPULAR SCIENCE REVIEW. 
end cell, or antheridia (fig. 5, b), of which contains these anthe- 
rozoids, each of which has a yellow spot in the centre. When 
the cell-wall breaks up, the latter bodies become free (fig. 5, c), 
and come in contact with the spore, or ovule (fig. 5, a). These 
are also found in the same cavity, among the roots of the 
branching antheridia. These spores thus become fertilised, and 
thus the mode resembles very much the enclosed flowers of the 
common fig. 
Let us see how this is carried out in the freshwater algae. 
We will take a very common instance, Vaucheria. It is com- 
posed of green filaments ; growing in ponds, on damp earth, 
in ditches — it does not particularly dislike, as most of the algae 
do, those which are fragrant, but flourishes freely, becoming a 
tangled mass of very tough fibres on the surface of the water. 
Although it slightly branches yet it is not jointed, and by this 
it may be known from almost every form with which it grows. 
It is indeed only one cell, sometimes attaining many inches in 
length. The chlorophyl, which is of a deep-green colour, is 
generally applied to the inner surface of the cell-wall ; at one 
end is found a sort of root of colourless branches, whereby it 
attaches itself to any objects. The other end of the branches is 
rather club-shaped, of much darker green, and more dense. 
Now to those who rise very early in the morning in summer, the 
following facts may be revealed by nature. A short distance 
from the club-shaped end (fig. 6, a), a line of separation may be 
observed ; after a time, the end of the tube bursts, and the con- 
tents now escape (fig. 6, 6), and assume an oval form, covered 
with minute vibrating hairs, or cilia, which propel the mass in a 
rotatory manner in the water (fig. 6, c). This may be called a 
zoospore ; perhaps, as it has a number of cilia all over its sur- 
face, it may be considered rather as an aggregation of ordinary 
zoospores."* After a few hours, this zoospore falls to the bottom 
of the vessel, loses its cilia, its walls become thicker, and soon 
after, a process arises from it, which is the beginning of another 
tube. This is a good example of one, perhaps the most common, 
plan by which these common forms are multiplied. This pro- 
cess is repeated rapidly, and thus this species increases fast. 
But this is not the mode which is analogous to that of the 
seaweed. This is accomplished by the following arrange- 
ment : — 
* At certain parts of the tube, the observer may find elevations 
springing from it in pairs (fig. 7), one of which is in the form of 
a hook, or crosier (fig. 7, a), the other oval, with or without a 
stem (fig. 7, b). Sometimes on the same stem there are more than 
one oval process. Now it is in the hook-like process that the 
* See paper on lC Volvox ” in this Review, vol. v. 
