millions of poisoned darts in a Jelly-fish? Who would guess that these
weapons are coiled up, ready to spring out at their prey? Men have made
many weapons for killing, from the bow-and-arrow to the torpedo, but
none of them is more wonderful than the weapon of the Jelly-fish.

EXERCISES

1. Where is the mouth of the Jelly-fish placed?

2. How does the Jelly-fish move through the water?

3. What is the food of the Jelly-fish?

4. How does it obtain its food?

[Illustration: SHELLS.

1. A FRESHWATER TURRET SHELL.

2. EDIBLE MUSSEL.

3. CONE SHELL.

4. SWORD-BLADE RAZOR-SHELL.

5. EAR SHELL, OR ORMER.

6. A TOP SHELL.

7. SCALLOP.

8. SWAN MUSSEL.]

LESSON X.

SHELLS AND THEIR BUILDERS (1).

THE PERIWINKLE, WHELK AND LIMPET.

Most of the shells which you find scattered over the shore are empty.
The little animals which built them are gone; and their empty houses, of
wonderful shapes and colours, are all that you find. Let us look at the
builders of these pretty homes.

The shell-builders have soft, juicy bodies, and they are put in one big
division of the animal kingdom--the _mollusca_, which only means
_soft-bodied_. Some of these molluscs do not build shells. But most of
them build a shelly house for themselves; they do this to defend their
soft bodies from the attacks of a host of enemies. Some build two
shells--the Oyster and Mussel do, as you know. These are called
_bi-valves_; that is, two valves or shells; and others, like the Garden
Snail, the Limpet, and Periwinkle, have one shell only, and so are
called _uni-valves_.

The crab, and other _crustaceans_, also have a hard covering to their
soft bodies; but it is not at all like the shell of a Snail, or other
_mollusc_. The Snail's shell is like the little boy's suit which is
altered and made bigger as the boy grows. The crab's covering is a suit
which cannot be altered. It must be thrown away, and replaced by a
larger one.

The body of the shell-builder is wrapped in a soft covering, a kind of
outer coat, which is called the _mantle_. Now this mantle is one of
Nature's cleverest inventions. It is able to take the substance called
_lime_ from the food of the animal, and to use it as building stuff.

[Illustration: PRECIOUS WENTLETRAP.]

The shell is built to fit the soft body. When a Periwinkle is hatched
from the egg, it is as big as a pin's head. It eats and grows, and the
shell must therefore be made larger. So the man