the cells and their mass. And each cell in our bodies lives in one
sense its own individual life, only bathed in the lymph and
receiving from it its food and oxygen instead of taking it from the
water.

But in another sense the cells of our body live an entirely
different life, for they form a community. Division of labor has
taken place between them, they are interdependent, correlated with
one another, subject therefore to the laws of the whole community or
organism. There are many respects in which it is impossible to
compare Robinson Crusoe with a workman in a huge watch factory; yet
they are both men.

Both the amoeba and we live in the closest relation to our
environment, and conformity to it is evidently necessary: life has
been defined as the adjustment of internal relations to external
conditions. We continually take food, use it for energy and growth,
and return the simpler waste compounds. We are all of us, as
Professor Huxley has said, "whirlpools on the surface of Nature;"
when the whirl of exchange of particles ceases we die. We have seen
that the fusion of two amoebæ results in a new rejuvenated
individual. Why is a mixture of two protoplasms better than one? We
can frame hypotheses; we know nothing about it. What of the mind of
the amoeba? A host of questions throng upon us and we can answer
no one of them. All the great questions concerning life confront us
here in the lowest term of the animal series, and appear as
insoluble as in the highest.

Our second ancestral form is also a fresh-water animal, the hydra.
This is a little, vase-shaped animal, which usually lives attached