THE aspect of paleontology has greatly changed since the time of Cuvier, when species were supposed to be fixed, and the curious monsters whose remains were unearthed from time to time were believed to be unchangeable, isolated entities. Now it is shown that fossil species are not thus independent, but are simply phases of development of types which are carrying on their evolution through the immensity of the ages. A plan has ruled in the vast and magnificent history of this evolution, and I purpose to tell what I believe I have discovered of it. I can not conceal that in the present state of science such an essay will be very imperfect. When I was traveling in the East I found the horizons in the morning veiled by the bluish mist which the poets are so fond of, and tried to discover the silhouettes of the beautiful marble mountains through them. So, in the morning of our paleontological science, we look upon the distances of life vaguely sketched, and try to distinguish a few lines of the plan that rules it. We discern but little, but that little is enough to charm us, as a glimpse of sunshine charms in a dark landscape.
It seems to me, further, that besides its philosophical interest, the inquiry into the plan of creation is of importance in practical geology. Up to this time the determination of the age of the earth has been empirical. It will become rational as soon as we are in possession of the plan of creation. Geologists will recognize that one of the best means of fixing the age of a formation is to know the stage of development of the fossils it contains.
The world of life is a grand unity, of which we can follow the development as we do that of an individual. When we follow the course of the immensity of geological times, we meet successive changes, and our mind goes on from surprise to surprise. Each epoch has its own physiognomy, and each phase of each epoch offers some variation; the days of the world follow one another and are not alike. Yet manifest as are the differences, they are not radical. Paleontology has not discovered any new branching or any new class or subclass.
From the primary ages, animated nature has had general traits of resemblance with existing nature. Sponges and polyps were already forming colonies, echinoderms were divided into five parts, insects were provided with three pairs of legs, arachnids had four, and myriapods had a multitude. M. Bernard Renault found in a coal bed an ostracode, the body of which is entirely preserved. A study of it made by M. Charles Brongniart showed the same details of organization as in our days. Numerous brachiopods