unequally divided tails. These scales are well preserved, and immense numbers of the bony head-plates of one of these fishes are found in rocks in the English Midlands and in Scotland. The bony-scaled fishes have few living descendants, but among them are the sturgeon, the bony pike which lives in the lakes of North America, and a curious fish which is found only in the Nile.

Later than the bony-scaled and shark-like fishessome twelve million years at a rough reckoning may

FOSSIL FISH

have lapsed between the first appearance of these two groups

-we find in the rocks of the coal measures the first amphibians, ancestors of the newts, salamanders, frogs, and toads of to-day. There was an immense variety of them, some being as large as a large crocodile ; they were the dominant animals of the coal forests, as later on the great reptiles and the mammals were successively supreme. By infinitely slow adaptations water animals, whose young remained fish-like in form and breathed by gills, became fitted for a swamp life. They acquired lungs, voice, and a movable tongue; the fishes' two pairs of fins became fore- and hind-legs, which, however, scarcely raised them from the ground; the webbed rays of the fins diminished to four or five, the ends of which remained free and formed fingers and toes.

Two stocks evolved from the newt-like forms of the earliest amphibians -one represented by the frogs, toads, and salamanders of to-day, animals still spending their early life in the water where they arose, the other the great reptile stock which in its heyday occupied a

position in the animal world comparable with that later on of the great mammals, the tigers, elephants, rhinoceroses, and giraffes. They reached their greatest development in the epoch immediately preceding that of the chalk rocks, and at their culminating point another group of animals destined to supplant them makes its appearance. One reptile stock had given rise to birds, the first warm-blooded animals; the other and more important warm-blooded group, the hairy-coated

SKELETON OF A DINOSAUR (BRONTOSAURUS)

mammals, destined to attain such size, strength, and variety, appeared among the great reptiles as small, rat-like creatures with, we may imagine, no sign of their great future about them. Yet the great reptiles inexplicably died out and only the smaller forms have living representatives in the crocodiles, tortoises, snakes, and lizards of to-day.

There were herb-eating reptiles, and carnivorous reptiles which preyed upon their vegetarian brethren. They had completely mastered locomotion on land, and some of them had even made the conquest of the air. Though at one time they had completely abandoned a water life, some of them went back to the sea, and by their huge bulk assumed a position among its denizens like that of present-day whales and porpoises. In all three elements they were the dominant animals.

The oldest members of the group were the theromorphs, some of whose bones bear so close a resemblance to those of mammals that they have been thought the possible ancestors of this group. They carried their bodies clear of the ground and probably had very much the movements of a dog. A skeleton of one of these, found in Cape Colony, is in the Natural History Museum at South Kensington. It is herbivorous from its teeth,

PROBABLE APPEARANCE OF PLESIOSAURUS SWIMMING
ON THE SURFACE OF THE WATER

and stands eight feet high. Other varieties resembled the rhinoceros in their huge tusks, or had strange crests. One carnivorous theromorph found on the banks of the river Dwina has a skull two feet long and huge tigerlike teeth.

However, the group of extinct reptiles which corresponds most closely to the great mammals-elephants, rhinoceroses, kangaroos, etc.-were the dinosaurs. There was a carnivorous stock, the lions and tigers of their day, though they were not the ancestors of the true lions and tigers, which, as has been mentioned, possibly descended from the theromorphs, and a vegetarian stock which they hunted. Some of the dinosaurs, both carnivorous and herbivorous, resembled

kangaroos in their habit of standing and partly running on their hind-legs only. Thus standing they could reach with their fore-legs shoots of trees twenty feet from the ground. The first skeleton of these kangaroolike dinosaurs was dug up in Sussex. Twenty-two huge skeletons were afterward found entire in a coal mine near Brussels, and seven of them were set up in the Brussels museum. A cast of one of these is in the Natural History Museum. Bird-like varieties of these dinosaurs no bigger than a gull existed at the same time as the great forms.

Some great dinosaurs went on all fours. One skeleton of this type dug up in Wyoming is eighty feet long. A good deal of its length is accounted for by a very long tail and a very long neck, bearing a head extremely .small in comparison, but its body is as big as that of a big elephant and its back is fourteen feet from the ground. There were extraordinary crested dinosaurs, as there were theromorphs, and again there were some that were like three-horned rhinoceroses in size and appearance.

The reptiles which after ages of evolution into land forms went back to the sea were the plesiosaurs and ichthyosaurs. In these the fore- and hind-legs which had been evolved from fins became paddles, but retained the structure of legs. The plesiosaur, which measured about thirty feet from snout to tail, had a long, swan-like neck and a long head furnished with pointed teeth. It no doubt preyed upon fish and probably upon the birds and lizards of the shore. The plesiosaur was extinct ages before the evolution of man, or it might have given rise to those legends of the sea-serpent which have persisted to the present day.

The ichthyosaurus had a long head and short neck, and strongly resembled the porpoises and grampuses among living whales. All these water reptiles used their tail as the chief swimming organ.

The flying reptiles-dragons of the air-were the pterodactyls, which varied in size from that of a robin to huge creatures with a twenty-foot spread of wing. Unlike birds, they had both fore- and hind-limbs clawed.

SKELETON OF ICHTHYOSAURUS PRESERVED IN LIASSIC ROCK

Their wings resembled those of a bat rather than those of a bird, since they were covered with a membrane instead of feathers. This membrane spread from one enormously elongated finger to the side of the body and the short hind-legs. From the great activity implied by flying it is probable that the pterodactyls had better lungs than are possessed by modern reptiles, whose torpid periods are due to changes of temperature combined with a breathing system far inferior to that of birds and mammals.

The remains of the great reptiles disappear from the rocks at the close of the chalk period. Why they died out we can only surmise. Modern reptiles are cold