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 _Nummulina_). 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.
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