Page:Popular Science Monthly Volume 50.djvu/550

532 belonged to genera which exist in our seas—such as Lingula, Rhynchonella, and Terebratula. Besides fishes of special types, we find some with tendencies toward those of to-day. Prof. Vaillant, examining a Permian genus which I had described under the name of Megopleuron, thought it was so nearly like some living ceratodes of Australia that he proposed to describe it under the same generic name. The Primary reptiles, although very different from those of our epoch, have many characters of resemblance to them. For example, having occasion to study in detail the reptiles of the Permian, I was very much struck by seeing that their heads had the same bones, both above and below, as in the existing animals. MM. Marcellin, Boule, and Glangeaud, comparing the paws of a reptile of the same formation with those of a common varanus, remarked their extreme similitude.

When we come to the Secondary formations, we find many invertebrate animals related to living genera. Most of the vertebrate animals are easily distinguished from present genera, though usually not because they present any unknown special features, but because they combine characteristics that are now distributed among distinct classes. M. Seeley has recently described Triassic quadrupeds from Africa which diminish the distance between the reptiles and the mammals; the icthyosaurus, which is cited as one of the most extraordinary fossils, recalls the fish in its vertebræ, the massive mammals in its fore flippers, and the reptiles in its other characteristics. Although the pterodactyl certainly belongs to the class of reptiles, its manner of flying is like that of flying mammals. The iguanodon is a reptile with its hinder limbs forerunners of those of birds. On the other hand, the archæopteryx is a bird with reptilian recollections. The Secondary fossils, which have surprised paleontologists so much by their singular features, in reality establish connections among animated beings instead of disclosing gaps.

In the Tertiary epoch the existing genera—rhinoceros, tapir, boar, gazelle, elephant, hyena, cat, bear, etc.—appear each in its turn. We find species, as well as genera, so near living forms that it is difficult not to suppose their near relationship.

Finally, the species of Quaternary times are for the most part identical with those of to-day, or so little different that they may be considered simply as races. It is impossible to mark a boundary between beings that existed before us and those that live with us.

It must therefore be recognized that the fossil world is not distinct from the existing world; there is only a single world, which has continued from the most ancient ages till our days. It can be studied as if it were an individual; in the same way as we