Besides the development of this wonderful series of animals, that we may call in a certain way our kindred, there have been several other remarkable advances in this Tertiary time, this age of crowning wonders in the earth’s history. The birds have gone forward very rapidly; it is likely that there were no songsters at the first part of this period, but these singing birds have developed very rapidly in later times. Among the insects the most remarkable growth is among the ants, the bees, and their kindred. These creatures have very wonderful habits; they combine together for the making of what we may call states, they care for their young, they wage great battles, they keep slaves, they domesticate other insects, and in many ways their acts resemble the doings of man. Coming at about the same time as man, these intellectual insects help to mark this later stage of the earth as the intellectual period in its history. Now for the first time creatures are on the earth which can form societies and help each other in the difficult work of living.
Among the mollusks, the most important change is in the creation of the great, strong swimming squids, the most remarkable creatures of the sea. Some of these have arms that can stretch for fifty feet from tip to tip.
Among the plants, the most important change has been in the growth of flowering plants, which have been constantly becoming more plenty, and the plants which bear fruits have also become more numerous. The broad-leaved trees seem to be constantly gaining on the forests of narrow-leaved cone-bearers, which had in an earlier day replaced the forests of ferns.
In these Tertiary ages, as in the preceding times of the earth, the lands and seas were much changed in their shape. It seems that in the earlier ages the land had been mostly in the shape of large islands grouped close together where the continents now are. In this time, these islands grew together to form the united lands of Europe, Asia, Africa, Australia, and the twin American continents; so that, as life rose higher, the earth was better fitted for it. Still there were great troubles that it had to undergo. There were at least two different times during the Tertiary age termed glacial periods, times when the ice covered a large part of the northern continents, compelling life of all sorts to abandon great regions, and to find new places in more southern lands. Many kinds of animals and plants seem to have been destroyed in these journeys; but these times of trial, by removing the weaker and less competent creatures, made room for new forms to rise in their places. All advance in nature makes death necessary, and this must come to races as well as to individuals if the life of the world is to go onward and upward.