of an apple, with the larvae of the insect
subsisting in its interior. Each of these widely different forms is
evoked from the oak leaf by the magic of an insect's ovipositor.
Chemically, the constituents of all of them are undoubtedly the same.

It is one of the most curious and suggestive things in living nature. It
shows how plastic and versatile life is, and how utterly unmechanical.
Life plays so many and such various tunes upon the same instruments; or
rather, the living organism is like many instruments in one; the tones
of all instruments slumber in it to be awakened when the right performer
appears. At least four different insects get four different tunes, so to
speak, out of the oak leaf.

Certain insects avail themselves of the animal organism also and go
through their cycle of development and metamorphosis within its tissues
or organs in a similar manner.

V

On the threshold of the world of living organisms stands that wonderful
minute body, the cell, the unit of life--a piece of self-regulating and
self-renewing mechanism that holds the key to all the myriads of living
forms that fill the world, from the amoeba up to man. For chemistry
to produce the cell is apparently as impossible as for it to produce a
bird's egg, or a living flower, or the heart and brain of man. The body
is a communal state made up of myriads of cells that all work together
to build up and keep going the human personality. There is the same
cooeperation and division of labor that takes place in the civic state,
and in certain insect communities. As in the social and political
organism, thousands of the citizen cells die every day and new cells of
the same kind take their place. Or, it is like an army in battle being
constantly recruited--as fast as a soldier falls another takes his
place, till the whole army is changed, and yet remains the same. The
waste is greatest at the surface of the body through the skin, and
through the stomach and lungs. The worker cells, namely, the tissue
cells, like the worker bees in the hive, pass away the most rapidly;
then, according to Haeckel, there are certain constants, certain cells
that remain throughout life. "There is always a solid groundwork of
conservative cells, the descendants of which secure the further
regeneration." The traditions of the state are kept up by the
citizen-cells that remain, so that, though all is changed in time, the
genius of the state remains; the individuality of