SECTION VII.
CLASSIFICATION OF ANIMALS AND PLANTS.
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.
SYNOPSIS OF GROUPS.
A. Protozoa. Unicellular animals, dissociated, or associated in simple, loose colonies of similar organisms. Many have an exoskeleton of lime, flint, or other material. Reproduction by fission and by temporary or permanent conjugation.
B. Metazoa. Multicellular animals, consisting of a large number of cells associated together to form single, complex individuals. The cells of an individual are usually differentiated into several kinds performing special functions. Reproduction in the higher forms is sexual; in the lower forms it is often by budding as well as sexual.