The Reptilia in their several orders are remarkable for absence of any modification of the arms which might suggest a capacity for acquiring wings, as being latent in their organisation. Crocodiles, Tortoises, and Serpents are alike of the earth, and not of the air. But among Lizards there are small groups of animals in which a limited capacity for movement through the air is developed. It is best known in the family of small lizards named Dragons, represented typically by the species _Draco volans_ found in the Oriental region of the East Indies and Malay Archipelago. The organ of flight is produced in an unexpected way, by means of the ribs instead of the limbs. The ribs extend outward as far as the arms can stretch, and the first five or six are prolonged beyond the body so as to spread a fold of skin on each side between the arm and the leg. The membrane admits of some movement with the ribs. This arrangement forms a parachute, which enables the animal to move rapidly among branches of trees, extending the structure at will, so that it is used with rapidity too quick to be followed by the eye, as it leaps through considerable distances. A less singular aid to movement in the air is found in some of the lizards termed Geckos. The so-called Flying Gecko (_Platydactylus homalocephalus_) has a fringe unconnected with ribs, which extends laterally on the sides of the body and tail, as well as at the back and front of the fore and hind limbs, and between the digits, where the web is sometimes almost as well developed as among Tree Frogs. This is essentially a lateral horizontal frill, extending round the body. Its chief interest is in the circumstance that it includes a membrane which extends between the wrist bones and the shoulder on the front of the arm. That is the only part of the fringe which represents the wing membrane of a bird. The fossil flying reptiles have not only that membrane, but the lateral membranes at the sides of the body and behind the arms. Other lizards have the skin developed in the direction of the circumference of the body. In the Australian Chlamydosaurus it forms an immense frill round the neck like a mediæval collar. But though such an adornment might break a fall, it could not be regarded as an organ of flight. FLYING BIRDS [Illustration: FIG. 8. POSITION OF BIRDS IN FLIGHT]