A SYNOPSIS OF THE ANIMAL KINGDOM.
In order that the reader may appreciate to some extent the relative positions of the different groups of animals, extinct and living, in the scale of life, the following brief classification may be useful. This synopsis is especially intended to help readers who are not familiar with elementary zoölogy to understand the significance of the different types of animals found in the strata of different geologic periods, and more particularly to grasp the meaning of the Diagram of Development. The animals are usually mentioned in the order of their position in the scale of life, commencing with the lowest and simplest.