in their structure and composition from an ordinary hen's egg, except
that there is no shell, only a skin provided with little fibers called
cilia, that project from it, and by the movement of these the embryo
sponge is able to propel itself through the water. It thus lives until
it has reached a certain stage of development, when it seeks out a
pebble or rock, to which it attaches itself at one end--preparation for
which has been made by its peculiar structure during its life when it
was free to float around through the water. It is now a prisoner and
chained to the rock it has selected for the foundation of its home.
Having no longer any use for the little cilia, which enabled it to swim
through the water, it now loses them. Here is a beautiful illustration
of how nature provides for the necessities of the smallest things, and
how when the necessity that demanded a certain condition passes by the
condition passes with it. The embryo begins to show a fibrous
development, which is the beginning of the framework of a new sponge.
Evolution goes on, every step of which is as mysterious as a miracle,
until the growing thing is a full-grown sponge, equipped with the means
for respiration, circulation, feeding, digestion, and reproduction.

Sponges grow in the bottom of the sea at different depths. They are
obtained by divers who make a business of gathering them. The best
sponges are called the Turkish sponge, which are very soft and velvety,
and may be bleached until they are nearly white by subjecting them to
the action of certain acids. The divers become very expert, but they do
not have the modern equipments of a diving suit. The Syrian divers in
the Mediterranean go down naked with a rope attached to their waists and
a stone attached to the rope to cause them to sink, together with a bag
for carrying the sponges. They have trained themselves until they can
remain under water from a minute to a minute and a half, and in that
time can gather from one to three dozen sponges. The ordinary depth to
which they descend is from eight to twelve fathoms. But a very expert
diver will go down as far as forty fathoms. The better class of sponges
are said to grow in the deeper waters. The coarse inferior sponges are
called the Bahama sponge. This sponge is of a peculiar shape, growing
more like a brush, with long bristly fiber.

The trade in sponges is quite large. The consumption in Great Britain
alone amounts to about $1,000,000