65:2.5

Before long the early single-celled animal types associated themselves in communities, first on the plan of the Volvox and presently along the lines of the Hydra and jellyfish. Still later there evolved the starfish, stone lilies, sea urchins, sea cucumbers, centipedes, insects, spiders, crustaceans, and the closely related groups of earthworms and leeches, soon followed by the mollusks—the oyster, octopus, and snail. Hundreds upon hundreds of species intervened and perished; mention is made only of those which survived the long, long struggle. Such nonprogressive specimens, together with the later appearing fish family, today represent the stationary types of early and lower animals, branches of the tree of life which failed to progress.