But even a single cell lends
itself to infinite variety of shape, and we have to penetrate to
the very lowest level of this luxuriant world of one-celled
organisms to obtain some idea of the most primitive living
things. Properly speaking, there were no "first living things."
It cannot be doubted by any student of nature that the microbe
developed so gradually 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.
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