Haeckel's second pedigree is as follows: - In representing pictorially the groups of the animal kingdom as the branches of a tree, it becomes obvious that a distinction may be drawn, not merely between the individual main branches, but further as to the level at which they are given off from the main stem, so that one branch or set of branches may be marked off as belonging to an earlier or lower level than another set of branches; and the same plan may be adopted with regard to the clades, classes and smaller branches.
