These cells are so minute that, of the smallest, some
hundreds would not cover the dot of a printed _i_ on this page.
They are of diverse shapes and contents, and perform various different
operations.
[Illustration: Fig 48.]
The first formation of every animal is accomplished by the agency of
cells, and may be illustrated by the egg of any bird or fowl. The
exterior consists of a hard shell for protection, and this is lined
with a tough skin, to which is fastened the yelk, (which means the
_yellow_,) by fibrous strings, as seen at _a_, _a_, in the diagram. In
the yelk floats the germ-cell, _b_, which is the point where the
formation of the future animal commences. The yelk, being lighter than
the white, rises upward, and the germ being still lighter, rises in the
yelk. This is to bring both nearer to the vitalizing warmth of the
brooding mother.
New cells are gradually formed from the nourishing yelk around the
germ, each being at first roundish in shape, and having a spot near
the centre, called the nucleus. The reason why cells increase must
remain a mystery, until we can penetrate the secrets of vital
force--probably forever.
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