Later on,
as we know, the egg or germ shows traces of structure in the case of
the higher animals and plants; while even lowly forms of life exhibit
more or less characteristic phases when they reach their adult stage.
But, of life's beginnings, the microscope is as futile as a kind
scientific touchstone for distinguishing animals from plants as is
power of movement, or shape, or form.
A fourth point of appeal in the matter is found within the domain of
the chemist. Chemistry, with its subtile powers of analysis, with its
many-sided possibilities of discovering the composition of things, and
with its ability to analyze for us even the light of the far distant
stars, only complicates the difficulties of the biologist. For, while
of old it was assumed that a particular element, nitrogen, was
peculiar to animals, and that carbon was an element peculiar to
plants, we now know that both elements are found in animals, just as
both occur in plants. The chemistry of living things, moreover, when
it did grow to become a staple part of science, revealed other and
greater anomalies than these. It showed that certain substances which
were supposed to be peculiar to plants, and to be made and
manufactured by them alone, were also found in animals.
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