great extinct reptiles had to do with the fact of their ceasing to exist. Animals with bigger and ever-increasing brains outdid them in the struggle for existence. It has already been noted that the crowding of the land may have led some reptiles to take to the sea. The same influence may have led others to take to the air and thereby escape the monsters of the swamps, jungles, and forests. Whatever the cause, the most striking and wonderful feature of this period was the development of flying reptiles. They had just been seen in the Trias. In the Jurassic they appeared fully developed. They doubtless sprang from some agile hollow-boned saurian, more or less akin to the slender leaping Dinosaurs. Between the ponderous Brontosaurs and the airy Pterodactyls was the most striking of contrasts. At first these bird-like reptiles were small, but later their wings had a spread of as much as twenty feet, veritable flying dragons. They were not adorned with feathers, but like bats had leathery membranes stretched from the fore limbs to the body and to the hind limbs. Their heads were bird-like, and their jaws at first were set with teeth. They had true powers of flight, as is shown by the discovery of their remains in places where they must have been far out at sea when they sank and were buried. Later Pterodactyls had no teeth, and were, perhaps, milder in habits. [Illustration: Archæopteryx (the earliest known fossil bird), and Compsognathus (a small Dinosaur)] It seems natural to pass from the fossil reptiles to the birds. But as a matter of fact the birds are not very closely related to the Pterodactyls, and seem to have been descended from some other very special form of reptiles, so peculiar as to be considered a distinct class. It may actually have been descended from those reptiles among the Dinosaurs which walked on their hind legs and had only three toes to the foot. The first bird found belongs to Jurassic times; and its skeleton, found in some slate remains at Solenhofen in Bavaria, is now to be seen in the Natural History Museum. There is another one in Berlin. This bird, called the _Archæopteryx_, was of the size of a large pigeon, had a short head apparently without a beak, and its jaws were armed with teeth. Whereas living birds have the fingers of their "hands" tied together in their wings, this bird has three distinct fingers at the corner of its wings, each armed with a claw. Its legs were like those of living birds, and it had four toes. Its tail was unlike that of any living bird, and like that of a lizard. Whereas the bony part of the tail of living birds is very short and bears the tail feathers set across it fanwise, the _Archæopteryx_ had a long bony tail made up of many bones, and the feathers were set in a series one behind the other till the tail looked like the leaf of a date palm in shape. Strange as this little creature appears it was a genuine bird, for it had these feathers well developed, as the two