ummulina_). The
shell, therefore, may be regarded, in such cases, as a more or
less completely porous calcareous structure, filled to its minutest
internal recesses with the substance of the living animal, and
covered externally with a layer of the same substance, giving
off a network of interlacing filaments.

[Illustration: Fig. 25.--The animal of _Nonionina_, one of the
_Foraminifera_, after the shell has been removed by a weak acid;
b, _Gromia_, a single-chambered Foraminifer (after Schultze),
showing the shell surrounded by a network of filaments derived
from the body substance.]

[Illustration: Fig 26.--Shells of living _Foraminifera_. a,
_Orbulina universa_, in its perfect condition, showing the tubular
spines which radiate from the surface of the shell; b, _Globigerina
bulloides_, in its ordinary condition, the thin hollow spines
which are attached to the shell when perfect having been broken
off; c, Textularia variabilis; d, Peneroplis planatus; e, Rotalia
concamerata; f, _Cristellaria subarcuatula._ [Fig. a is after
Wyville Thomson; the others are after Williamson. All the figures
are greatly enlarged.]]

Such, in brief, is the structure of the living _Foraminifera_;
and it is believed that in _Eozooen_ we have an extinct example of
the same group, not only of special interest from its immemorial
antiquity, but hardly less striking from its gigantic dimensions.
In its original condition, the entire chamber-system of _Eozooen_
is believed to have been filled with soft structureless living
matter, which passed from chamber to chamber through the wide
apertures connecting these cavities, and from tier to tier by
means of the tubuli in the shell-wall and the branching canals
in the intermediate skeleton. Through the perforated shell-wall
covering the outer surface the soft body-substance flowed out,
forming a gelatinous investment, from every point of which radiated
an interlacing net of delicate filaments, providing nourishment
for the entire colony. In its present state, as before said,
all the cavities originally occupied by the body-substance have
been filled with some mineral substance, generally with one of
the silicates of magnesia; and it has been asserted that this
fact militates strongly against the organic nature of _Eozooen_,
if not absolutely disproving it. As a matter of fact, however--as
previously noticed--it is by no means very uncommon at the present
day to find the shells of living species