eet from the table on which the specimen rested."

Dr. Peysonell, who paid great attention to the structure of the sponge,
brought proofs of its animal vitality before the Royal Society in the
years 1752--57. And Mr. Ellis, five years afterward, by his dissections,
set the question quite at rest; though he fell into the error of
believing that the frame of the sponge was the outer case of worms or
polypes. Later examination, however, has shown that the _frame_ or
_sponge_, commonly so called, is an _internal_ skeleton, while the vital
power is simply composed of a slimy film which coats over every fibre,
and which, inert as it appears, possesses the power of secreting the
particles essential to its growth.

It has been affirmed, that the sponge is observed to contract or shrink
when torn from the rooks; but there is satisfactory evidence to prove
that neither this nor any degree of laceration has a sensible effect on
this nerveless though vital mass.

All sponges, however, have not a horny framework, but some, which are
thereby rendered useless in a commercial point of view, are supported by
a skeleton composed of siliceous particles imbedded in a tough, fibrous
material. These particles, or _spicula_, as they are termed, are so
uniform in the species to which they severally belong, that, in the
words of Professor Grant, if the soft portion be destroyed, and a "few
of them brought from any pan of the world on the point of a needle, they
would enable the zoologist to identify the species to which they
originally belonged." Professor R. Jones, however, considers that this
opinion should be received with considerable limitations.

The last fact, trivial as it appears, assumes immense importance when we
learn that to these spicula we must turn for an explanation of the
isolated masses of flint which abound in various chalk formations. "The
mere assertion," says Rhymer Jones, "that flints were sponges, would no
doubt startle the reader who was unacquainted with the history of these
fossil relics of a former ocean;" and yet a little reflection "will
satisfy the most skeptical." For long ages the sponge is imbedded in the
chalk, through which water is continually percolating. A well-known law
of chemistry explains why similar matter should become aggregated; and
thus the siliceous matter of the sponge forms a nucleus for the
siliceous matter contained in the water, until at length the entire mass
is converted into a solid f