rrent of
water is maintained. From hence all faecal and other matter is
discharged through the oscula, the larger openings observed on the
surface of the sponge. Dr. Ledenfeld showed the different parts of
sponges by means of microscopic slides thrown on to a screen, and also
the shape and arrangement of the chambers in different species. The
ciliated chambers especially attracted attention. They are very small
and circular, and the interior is clothed with cells very similar to the
cilia cells in higher animal life.

These cells are arranged around the ciliated chambers in the form of a
collar, and from each cell flagella protrude, which are in continual
motion. These flagella, like bats' wings, are capable of being bent in
only one direction, so that, in the course of their pendulum-like
motion, in the movement one way the flagella are bent, while in the
return movement they remain stiff, thus causing a current of water
always flowing in one and the same direction. These ciliated chambers
are easily detected in the sponge by means of a microscope, as they
appear more highly colored. After the lecturer had thus given a general
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