sight. The four threads would be spread out, but if I
were to breathe on the glass, these threads would coil themselves
round the oval body; but as soon as the effect of the moisture had
passed away, the threads would shoot out again in the same position as
they were at first, causing the spore to leap as if it were alive.
The stems are of two kinds, fertile and unfertile; the one you have in
your hands is a fertile spike, and appears only in the spring; the
unfertile ones have no dust-like fruit, and have numerous jointed
branches growing in rows, or whorls as they are termed, round them;
they remain throughout the summer, and in some places form quite a
thick cover. Feel how rough the stem is; this is due to the presence
of a quantity of silex or flint in it; on this account some of the
species are used for polishing purposes. One kind, under the name of
"Dutch rushes," is imported from Holland, being used for polishing
mahogany, ivory, metal, &c. The horse-tails for the most part grow in
moist ground, in ditches and on the borders of lakes; some, however,
are common in corn fields and on the roadside. In this country they do
not attain a height of more than a few feet, but in tropical countries
one or two species grow to the height of sixteen feet or more.

[Illustration: HYDRAE, ON ROOTS OF DUCKWEED.]

Now for a dip with the bottle in this pond. I will try and catch a few
Hydrae. Strange animals, indeed, they are, and strange is their
history; but let us catch a few first. Nothing yet in my bottle like a
hydra. Ah! now we have one or two. You see a small creature sticking
to the stem of a bit of duckweed; around its mouth are five or six
little projections. At present they are contracted; but the hydra is
able to lengthen them out, when they appear as long, thin lines, which
are used as the creature's fishing-lines; it is not much larger than a
pin's head at present, but it can stretch its body out as it does its
lines. I will take a handful of duckweed, and put it, dripping wet,
into this bag, and when we get home we will place the whole in a glass
vessel full of water. In the course of half an hour or so, we shall,
no doubt, see several hydrae, probably of different species, in various
attitudes--some hanging loosely down, others erecting themselves in
graceful curves and throwing out their arms or tentacles many times
longer than their bodies; others shooting up their arms right above
their heads; others contrac