tion of the human organism, in that state in which it has
but just become distinguishable from the egg in which it arises, it is
nothing but an aggregation of such corpuscles, and every organ of the body
was, once, no more than such an aggregation.

Thus a nucleated mass of protoplasm turns out to be what may be termed the
structural unit of the human body. As a matter of fact, the body, in its
earliest state, is a mere multiple of such units; and, in its perfect
condition, it is a multiple of such units variously modified.

But does the formula which expresses the essential structural character of
the highest animal cover all the rest, as the statement of its powers and
faculties covered that of all others? Very nearly. Beast and fowl, reptile
and fish, mollusk, worm, and polyp, are all composed of structural units
of the same character, namely, masses of protoplasm with a nucleus. There
are sundry very low animals, each of which, structurally, is a mere
colorless blood-corpuscle, leading an independent life. But, at the very
bottom of the animal scale, even this simplicity becomes simplified, and
all the phenomena of life are manifested by a particle of protoplasm
without a nucleus. Nor are such organisms insignificant by reason of their
want of complexity. It is a fair question whether the protoplasm of those
simplest forms of life which people an immense extent of the bottom of the
sea would not outweigh that of all the higher living beings which inhabit
the land put together. And in ancient times, no less than at the present
day, such living beings as these have been the greatest of rock-builders.

What has been said of the animal world is no less true of plants. Imbedded
in the protoplasm at the broad, or attached, end of the nettle hair, there
lies a spheroidal nucleus. Careful examination further proves that the
whole substance of the nettle is made up of a repetition of such masses of
nucleated protoplasm, each contained in a wooden case, which is modified
in form, sometimes into a woody fibre, sometimes into a duct or spiral
vessel, sometimes into a pollen grain, or an ovule. Traced back to its
earliest state, the nettle arises, as the man does, in a particle of
nucleated protoplasm. And in the lowest plants, as in the lowest animals,
a single mass of such protoplasm may constitute the whole plant, or the
protoplasm may exist without a nucleus.

Under these circumstances it may well be asked, how is one mass