The science of life : fully illustrated in tone and line and including many diagrams

BOOK 2

but not all types, the head and limbs can be withdrawn. ‘The third is by far the largest and most varied order, and includes the snakes and lizards—the rattlesnakes, cobras, kraits, pythons, geckos, skinks, chameleons, monitors, iguanas, slow-worms, and a host of others. Finally, the fourth order contains one genus only—the lizard-like Sphenodon, which is sufficiently distinct in its internal anatomy to be put in an order by itself.

With the extinct reptiles—twenty orders of them !—we shall deal more fully later on. Most of the extinct reptiles, like the survivors of the group, were terrestrial, but some, the ichthyosaurs, plesiosaurs, and mosasaurs, lived like whales in the sea, and others, the pterodactyls, soared like bats by means of their elongated arms and fingers. The great and varied group of dinosaurs included (besides a number of smaller forms) the largest known land animals—animals second only to the whales in size; some of them peaceful browsers upon plants, others perhaps the fiercest and most terrible predatory creatures that the world has ever seen.

In that reptilian world of the past there may have been very different conditions from those prevalent to-day. Not only were the great animals of that time unprotected against wide variations of temperature, but the vegetation also was of a different

THE SCIENCE OF LIFE

fig. 75. The Green Lizard (Lacerta viridis).

CHAPTER 1

kind. There were no deciduous trees to shed their leaves in winter, if winter there was, and no conifers with a foliage able to resist injury from a heavy fall of snow. Nor were there grasses and flowers ripening seeds that could hibernate through a cold season. And all the surviving reptiles of to-day live either continuously in warm climates or with intermittent stages of winter torpor, for the summer sunshine. They are extraordinarily like the vestiges of some ancient conservative aristocracy living on in a world of harder conditions and more energetic newcomers.

§ 3d The Linking Amphibians

Frogs and salamanders are often classified by the uninitiated as reptiles, together with lizards and other cold-blooded land vertebrates. But they are not so. They belong to a very different class, the Amphibia—a class which is interesting because it sits on the fence that divides the lunged and limbed from the gilled and finned, the air-breathing mammals, birds, and reptiles from the water-breathing fishes. It is a class of vast antiquity, but never has it displayed the variety and abundance of the mammals and birds of recent times, nor of the reptiles

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