Look over the side of a boat, or
from the pier, and you often see them drifting by, hundreds of them,
like so many ghosts.
Each one is moving along, with its edges partly opening and shutting. It
is plain that this waving motion causes the creatures to move through
the water. Also, they can rise to the surface, or fall to the depths,
and do not collide with one another. So the Jelly-fish is not at all
helpless.
At night Jelly-fishes sometimes look very beautiful. Each one shines in
the water, with a soft yet strong light, like fairy lamps afloat in the
sea.
They are of all sizes. Some you could put in a small wineglass, others
measure nearly two feet across. Evidently the Jelly-fish grows, and, in
order to live and grow, it must eat; but what does it eat, and how does
it obtain its food?
[Illustration: MEDUSA.]
Before noticing the wonderful way in which this animal finds its dinner,
let us look at its body. In any large Jelly-fish you can see marks which
run from the centre of the body, and another mark round the edge of the
"umbrella." These are really tubes. They all join with a hollow space
inside the body, which is the creature's stomach.
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