Under such explanations of the mutual relations of the parts of animals, and groups of animals, time ceases to be a factor of primary importance in their construction or elaboration. The supposed necessity for practically unlimited time to produce changes in the vital organs which separate animals into great orders or classes is a nightmare, born of hypothesis, and may be profitably dismissed. The geological evidence is too imperfect for dogmatism on speculative questions; but the nature of the affinities of Ornithosaurs to other animals has been established on a basis of comparison which has no need of theory to justify the facts. It is not improbable that the primary epoch of time, even as known at present, may be sufficiently long to contain the parent races from which Ornithosaurs and all their allies have arisen. In thus stating the relation of Ornithosaurs to other animals the Flying Reptile has been traced home to kindred, though not to its actual parents or birthplace. There is no geological history of the rapid or gradual development of the wing finger, and although the wing membrane may be accepted as its cause of existence, the wing finger is powerfully developed in the oldest known Pterodactyles as in their latest representatives. Pterodactyles show singularly little variation in structure in their geological history. We chronicle the loss of the tail and loss of teeth. There is also the loss of the outermost wing digit from the hind foot as a supporter of the wing membrane. But the other variations are in the length of the metacarpus, or of the neck, or head. One of the fundamental laws of life necessitates that when an animal type ceases to adapt its organisation and modify its structures to suit the altered circumstances forced upon it by revolutions of the earth's surface its life's history becomes broken. It must bend or break. The final disappearance of these animals from the earth's history in the Chalk may yet be modified by future discoveries, but the Flying Reptiles have vanished, in the same way as so many other groups of animals which were contemporary with them in the Secondary period of time. Such extinctions have been attributed to catastrophes, like the submergence of land, so that the habitations of animals became an area gradually decreasing in size, which at last disappeared. It appears also to be a law of life, illustrated by many extinct groups of animals, that they endure for geological ages, and having fought their battle in life's history, grow old and unable to continue the fight, and then disappear from the earth, giving place to more vigorous types adapted to live under new conditions.