of
their small size, quite unable to force their way against strong
currents. Thus, on the outgoing tide, they would be swept off to sea,
and would die even before this was reached--as soon, indeed, as the
water became really salt. So, to prevent such a disaster, the
fresh-water mussel carefully nurses her young between her gills, till
they are old enough to help themselves. You will be surprised when I
tell you the strange device they have come to adopt, so soon as they are
cast adrift, whereby they may complete their days of infancy. Shielded
throughout the winter months, they are turned adrift on the first warm
day of Spring, a troop of very lively youngsters indeed. Each is encased
in a very wonderful shell (S in the figure in the top left-hand corner
of the illustration), quite unlike that of their parents, being
triangular in shape, and armed with a pair of pointed teeth (T). By
means of powerful muscles this shell is made to open and shut with great
rapidity, and thus the body of the little creature is quickly driven
through the water in a series of spasmodic jumps. Then comes a period of
rest, obtained by using the long thread or 'byssus' (B) as a float, this
thread being thrown out along the surface of the water. Then the hunt
for a host begins again. On and on they go, till one after
another--'curiouser and curiouser!'--seizes hold of a fish by means of
its hooks. Having caught hold tight, each clings like grim death, and as
a result of the irritation set up in the poor fish's skin, swelling
follows and soon grows up all round the young mussel, and makes him a
prisoner. But this is just what he wants. Snugly tucked away in his
living cradle he slowly assumes his adult shape, and at last bursts his
prison and falls to the bottom!

[Illustration: Fresh-water Mussels.]

There is yet another reason for this very strange and somewhat cruel
procedure. The love of self, among the lower animals, is so strong that
parents always drive away their young so soon as they become capable of
feeding, and fending for themselves; because, if they did not adopt
stern measures of this sort, famine and disease would be the result,
owing to overcrowding. On the whole, this banishment is not so hard as
it looks, the young having no sentiment for the place of their birth,
and being probably more capable of migrating than the parents. But the
method adopted by the fresh-water mussel is wasteful and dangerous;
wasteful, because thou