The _Cambrian_ period was the time of the establishment of the chief stocks of backboneless animals such as sponges, jellyfishes, worms, sea-cucumbers, lamp-shells, trilobites, crustaceans, and molluscs. There is something very eloquent in the broad fact that the peopling of the seas had definitely begun some thirty million years ago, for Professor H. F. Osborn points out that in the Cambrian period there was already a colonisation of the shore of the sea, the open sea, and the deep waters. The _Ordovician_ period was marked by abundant representation of the once very successful class of Trilobites--jointed-footed, antenna-bearing, segmented marine animals, with numerous appendages and a covering of chitin. They died away entirely with the end of the Palaeozoic era. Also very notable was the abundance of predatory cuttlefishes, the bullies of the ancient seas. But it was in this period that the first backboned animals made their appearance--an epoch-making step in evolution. In other words, true fishes were evolved--destined in the course of ages to replace the cuttlefishes (which are mere molluscs) in dominating the seas. _______________________________________________________________________ _RECENT TIMES_ Human civilisation. _______________________________________________________________________ {PLEISTOCENE OR GLACIAL TIME Last great Ice Age. _CENOZOIC ERA_ {MIOCENE AND PLIOCENE TIMES Emergence of Man. {EOCENE AND OLIGOCENE TIMES Rise of higher mammals. _______________________________________________________________________ {CRETACEOUS PERIOD Rise of primitive mammals, { flowering plants, { and higher insects. _MESOZOIC ERA_ {JURASSIC PERIOD Rise of birds and flying { reptiles. {TRIASSIC PERIOD Rise of dinosaur reptiles. _______________________________________________________________________ {PERMIAN PERIOD Rise of reptiles. {CARBONIFEROUS PERIOD Rise of insects. {DEVONIAN PERIOD First amphibians. _PALAEOZOIC ERA_ {SILURIAN PERIOD Land animals began. {ORDOVICIAN PERIOD First fishes. {CAMBRIAN PERIOD Peopling of the sea. _______________________________________________________________________ _PROTEROZOIC AGES_ Many of the Backboneless stocks began. _ARCHAEOZOIC AGES_ Living creatures began to be upon the earth. _______________________________________________________________________