able us to decide upon its true position in the animal kingdom.
Those who wish to study this interesting subject in detail must
consult the admirable memoirs by Dr W. B. Carpenter and Principal
Dawson: it will be enough here to indicate the results which
have been arrived at. The only animals at the present day which
possess a continuous calcareous skeleton, perforated by pores
and penetrated by canals, are certain organisms belonging to
the group of the _Foraminifera_. We have had occasion before
to speak of these animals, and as they are not conspicuous or
commonly-known forms of life, it may be well to say a few words
as to the structure of the living representatives of the group.
The _Foraminifera_ are all inhabitants of the sea, and are mostly
of small or even microscopic dimensions. Their bodies are composed
of an apparently structureless animal substance of an albuminous
nature ("sarcode"), of a gelatinous consistence, transparent, and
exhibiting numerous minute granules or rounded particles. The
body-substance cannot be said in itself to possess any definite
form, except in so far as it may be bounded by a shell; but it
has the power, wherever it may be exposed, of emitting long
thread-like filaments ("pseudopodia"), which interlace with one
another to form a network (fig. 25, b). These filaments can be
thrown out at will, and to considerable distances, and can be
again retracted into the soft mass of the general body-substance,
and they are the agents by which the animal obtains its food.
The soft bodies of the _Foraminifera_ are protected by a shell,
which is usually calcareous, but may be composed of sand-grains
cemented together; and it may consist of a single chamber (fig.
26, a), or of many chambers arranged in different ways (fig.
26, _b-f_). Sometimes the shell has but one large opening into
it--the mouth; and then it is from this aperture that the animal
protrudes the delicate net of filaments with which it seeks its
food. In other cases the entire shell is perforated with minute
pores (fig. 26, e), through which the soft body-substance gains
the exterior, covering the whole shell with a gelatinous film
of animal matter, from which filaments can be emitted at any
point. When the shell consists of many chambers, all of these are
placed in direct communication with one another, and the actual
substance of the shell is often traversed by minute canals filled
with living matter (e.g., in _Calcarina_ and _N