In those long ages when there were no human beings in the world and the lower orders of animals had the globe all to themselves, each successive period of change was distinguished by some special class of living creatures, which were then chief in numbers and importance. Each of these in its own age reached its prime in size and dominion. But while these particular families passed away at the close of their earth age, the classes to which they belonged frequently survived in changed forms, which have continued to the present. These late descendants of the old time possessors of the world have generally decreased in size and numbers, and increased in beauty and in capacity for ministering in some way to humanity. [Illustration: CHILDREN OF THE DAWN.] But there are some ancient classes of living creatures which have changed very little, and are to-day practically what they were at their origin. Thus the foraminifera were among the very earliest of living creatures, as they were also among the smallest, the most simple in structure, and the most widely distributed. Their work seemed to be first to collect material from sea-water to build into their own forms, and then to bequeath themselves to the formation of rock. There is no family of creatures so ancient, for beside them all other fossils seem modern. As living animals they still survive in almost unchanged conditions, and abound everywhere except in the Polar seas. In the tropics they are found in shallower waters than in the temperate zones. The hard name of these creatures comes from the word _foramen_, a little hole like the eye of a needle. Now these queer animals were made of a soft substance like jelly or glue in shells with many divisions. The walls of the lime-cells or rooms were full of tiny holes like the holes in a sieve, and through these the jelly part of the animal poured itself, and so filled and pervaded all the chambers or cells. Many of these creatures can be seen only through a microscope. In a former lesson we spoke of the nummulites, large specimens of this same order, and of their work in stone-making. We found that most of the building-stone of Paris, vast beds of stone in India, and a large part of the chalk rocks are nummulitic. The great pyramids of Egypt and the enormous terraces upon which they stand are built of the same nummulitic limestone, while many other vast ledges of limestone rock are composed of the minute shells of foraminifera. In most ancient times the coral polyps were building up their towers, and were perhaps larger and more plentiful in the lower Silurian age than at any other period; but coral polyps are still busy on the Pacific sea building their beautiful islands or atolls.