But to our story. You must allow me to tell this in my own way, which I
shall do by asking you to go to the nearest pond, get a bottle full of
water and weeds, and stand it in the light for an hour or so. Then look
carefully on the side of the bottle next the light for some tiny little
creatures about half an inch long, with slender stalked bodies, attached
by one end to the glass, and provided at the other by long, very
delicate, slowly-moving arms: you must seek, in short, for a creature
such as that shown in the picture as if seen under the microscope,
sticking to a piece of weed (fig. 2). At the top end of the stalk is the
mouth, and if you watch carefully you may be fortunate enough to see the
long arms catch a water-flea, and carry it towards the mouth. This
creature is known as the hydra. In some cases you will see two or even
three of these creatures all attached to the same stalk, and if you
watch every day, you will at last find that sooner or later this
partnership is dissolved, so that the branched hydra has split up into a
number of separate individuals--just as many as there were branches.

Now, the fresh-water hydra has some very near relatives which live in
the sea, and these fashion their lives on very different lines. In the
first place, they, like the hydra, start as single individuals, but
sooner or later develop little buds which grow out into arm-bearing
creatures exactly like themselves; but these, instead of breaking off as
in the hydra, remain fixed and themselves produce branches, which again
branch, and so on, until, as you will readily see, in a very short time
a colony of animals is produced which bears a remarkable resemblance to
a little tree! Such for example as you will see in fig. 4, growing
upside down!

[Illustration: HYDRA Fig. 2.]

You will have noticed that the fresh-water hydra had a wonderfully
elastic body, so that when frightened, as by a tap on the bottle, it
suddenly pulls itself down into a mere speck of jelly (fig. 2). This
feat its sea-dwelling cousins cannot perform, since, frail as they are,
some support became necessary when they took to the tree-like habit of
growth, and this support is found by encasing the whole body and its
branches in an outer coat of a horny, transparent character, with a hole
at the top of each branch expanded to form a cup to guard the long arms.
So then, when alarmed, all they can do is to draw down the arms into the
cup. In the illustrat