Let us pass to the secondary evolution considered in itself. It
involves two great features, -- differentiation and the increase of
definiteness through segregation. The differentiation is a cumulative
process, due to the fact that a plastic body keeps the traces of what
has happened to it, and so constantly prepares a basis for new
varieties of effects to be produced upon its various parts.
The segregation is due to the sorting types of forces, such as
were exemplified in our summary.