layer (the nucleus) and then later round this a second layer (the cell
substance)" (p. 213). The outermost layer of the cell usually thickens
to form the membrane, but this membrane formation does not always occur,
and the membrane is not present in all cells. The nucleus is formed in
exactly the same manner as the cell, and it might with much truth itself
be called a cell--a cell of the first order, while ordinary nucleated
cells might be designated cells of the second order (p. 212). In
anucleate cells there is probably only a single process of layer
formation round an infinitely small nucleolus. In almost all nucleate
cells the nucleus is resorbed when the cell reaches its full
development, and it is larger and more important the younger the cell
is.

The cell was for Schwann not a morphological concept at all, but a
physiological; the cell was a dynamical, not a statical unit.
Cell-formation was the process at the back of all production of life,
and cells were the centres of all vital activity. Each cell was itself
an organism, and its life and activities were to some extent independent
of the lives and activities of all the other cells. The multicellular
organism was a colony of unicellular organisms, and its life was a sum
of the lives of its constituent elements. This "theory of the organism,"
which holds so important a place in biology even at the present day, is
developed by Schwann in the concluding pages of his book.

He begins by contrasting the teleological with the materialistic
conception of living things. In the teleological view, a special force
works in the living organism, guiding and directing its activities
towards a purposeful end. According to the materialistic view there are
no other forces at work in the living organism than those which act in
the inorganic realm, or at least there are none but forces at one with
these in their blindness and necessity. True, the purposiveness of
living processes cannot be denied; but its ground lies, according to
this view, not in a vital force which guides and rules the individual
life, but in the original creation and collocation of matter according
to a rational plan. The purposiveness of life is part of the
purposiveness of the universe; just as the stars circle for ever in
harmoniously adjusted paths, so do the processes of life work together
towards a common end. Both are the inevitable result of the original
distribution of matter in the primitive chaos