ually
that it is as impossible to fix a precise term for the beginning of life
as it is to say when the night ends and the day begins. In the course of
time little one-celled living units appeared in the waters of the earth,
whether in the shallow shore waters or on the surface of the deep is a
matter of conjecture.

We are justified in concluding that they were at least as rudimentary
in structure and life as the lowest inhabitants of nature to-day. The
distinction of being the lowest known living organisms should, I think,
be awarded to certain one-celled vegetal organisms which are very common
in nature. Minute simple specks of living matter, sometimes less than
the five-thousandth of an inch in diameter, these lowly Algae are so
numerous that it is they, in their millions, which cover moist surfaces
with the familiar greenish or bluish coat. They have no visible
organisation, though, naturally, they must have some kind of structure
below the range of the microscope. Their life consists in the absorption
of food-particles, at any point of their surface, and in dividing into
two living microbes, instead of dying, when their bulk increases. A very
lowly branch of the Bacteria (Nitrobacteria) sometimes dispute their
claim to the lowest position in the hierarchy of living nature, but
there is reason to suspect that these Bacteria may have degenerated from
a higher level.

Here we have a convenient starting-point for the story of life, and
may now trace the general lines of upward development. The first great
principle to be recognised is the early division of these primitive
organisms into two great classes, the moving and the stationary. The
clue to this important divergence is found in diet. With exceptions
on both sides, we find that the non-moving microbes generally feed on
inorganic matter, which they convert into plasm; the moving microbes
generally feed on ready-made plasm--on the living non-movers, on each
other, or on particles of dead organic matter. Now, inorganic food is
generally diffused in the waters, so that the vegetal feeders have no
incentive to develop mobility. On the other hand, the power to move
in search of their food, which is not equally diffused, becomes a most
important advantage to the feeders on other organisms. They therefore
develop various means of locomotion. Some flow or roll slowly along
like tiny drops of oil on an inclined surface; others develop minute
outgrowths of their substanc