outline of the structure of the sponge, he drew attention to the
character of its food and its method of digestion. It is not known
exactly what the sponge lives upon, but if upon other animals they must
be necessarily very small, owing to the size of its inhalent pores.

The sponge, like the tape-worm, has no stomach, but must absorb its food
through the outer skin from matter in a soluble state, similarly to the
roots of trees. This process of absorption is probably accomplished in
the interradial or ciliated chambers, more probably in the former, as
the latter are generally considered excretory in function. Lime or
silica must also be absorbed from the water by most sponges in order to
make up the skeleton. The skeleton of calcareous sponges consists of a
number of spicules composed of carbonate of lime. These spicules are of
very varied though regular shape, but ordinarily assume a rod-like
needle shape or else a stellate form. In silicious sponges the spicules
are composed of silica, and are generally deposited around axial rods in
concentric layers. The spicules are joined together and cemented by a
body that has been named "spongin," which has much the same chemical
composition as silk, and, like silk, is very elastic. In some varieties
of sponges, especially in the kinds which come into the market, the
skeleton is almost entirely composed of fibers of pure "spongin." These
fibers are so close together as to draw up water by capillary action,
and, indeed, a great deal in the value of a sponge depends upon the
fineness and tenuity of these fibers.

Dr. Ledenfeld again illustrated this stage of his lecture by means of a
number of microscopic slides in which the variety of shape and size of
these spicules and "spongin" fibers were shown. The spicules are some
crutch-like, others spined or echinated, while the deep-sea sponges
appear to grow long thick spicules, which attach the sponge to the