&fist; All cells have their origin in the primary cell from
which the organism was developed. In the lowest animal and
vegetable forms, one single cell constitutes the complete
individual, such being called unicelluter orgamisms. A
typical cell is composed of a semifluid mass of protoplasm, more
or less granular, generally containing in its center a nucleus
which in turn frequently contains one or more nucleoli, the whole
being surrounded by a thin membrane, the cell wall. In some
cells, as in those of blood, in the amœba, and in embryonic
cells (both vegetable and animal), there is no restricting cell
wall, while in some of the unicelluliar organisms the nucleus is
wholly wanting. See Illust. of Bipolar.
Air cell.
See Air cell. --
Cell development (called also cell
genesis, cell formation, and cytogenesis), the
multiplication, of cells by a process of reproduction under the
following common forms; segmentation or fission,
gemmation or budding, karyokinesis, and
endogenous multiplication. See Segmentation,
Gemmation, etc. --
Cell theory.
(Biol.) See Cellular theory, under
Cellular.Cell (s&ebreve;l), v.
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