Jump to Navigation    [image:13569 align=left hspace=1]Sponges
present a point still somewhat problematical as to their true
position in the scale of animal life, and there are still many
doubtful or imperfectly known facts pertaining to their
organization. As a family, sponges are very remarkable for the
lack of a definite and constant form, have various habits of
growth, are insensible to irritation and powerless to move
about. The known species number now about three hundred, and new
ones are constantly observed, in view of which fact it is
obviously impossible to describe, within the limits of this
sketch, more than the prominent characteristics of the type. The
description following may be referred more particularly to the
sponges of commerce.  Milne-Edwards and others have considered
each sponge as one separate and distinct individual; but Prof.
Clarke, Dr. Lockwood, Prof. Grant and others, regard them as an
aggregation of minute infusoria, each within its living cell,
and they are considered to begin l