We shall all allow that the Tortoises are the most singular of any, and it is curious that they are also in many ways the nearest to the frogs and newts, although they are true reptiles. Slow ponderous creatures, with hard bony heads (Fig. 20), wide-open expressionless eyes, horny beaks, and thick clumsy legs, the tortoises seem at first sight to be only half alive, as they lumber along, “Moving their feet in a deliberate measure Over the turf,” carrying their heavy shell, and eating, when they do eat, in a dull listless kind of way. They do, in truth, live very feebly, for they can only fill their lungs with air by taking it in at the nostrils and swallowing it as frogs do, and then letting it drift out again as the lungs collapse, for their hard shell prevents them from pumping it in and out by the movement of their ribs like other reptiles. This slowness of breathing and the fact that they have only three-chambered hearts like frogs (see p. 76), so that the good and bad blood mix at every round, causes them to be very inactive, and they digest their food very slowly, and have been known to live months and even years without eating. [Illustration: Fig. 20. The Greek Tortoise.] This sluggishness would, indeed, certainly be their ruin in a bustling greedy world, if it were not for the strong box in which they live. Take in your hand one of the small Greek[72] or American[73] tortoises, so often sold as pets, and you will see how well he can draw back out of harm’s way, while at the same time you will, I think, be sorely puzzled to understand how he is made. His head, his four legs, and his tail, with their thick scaly skin, are intelligible enough. But why do all these grow on to the inside of his shell, so that when you trace them up you cannot find the rest of his soft body? You would hardly guess that his shell _is_ the rest of his body, or at least of his skeleton. But it is so. The arched dome which covers his back is made of his backbone and ribs, and the shelly plates arranged over it are his skin hardened into horny shields, which, in the Hawksbill turtle, form the tortoise-shell which is peeled off for our use; while the flat shell under his body is the hardened skin of his belly, and the bones which belong to it. [Illustration: Fig. 21. Carapace of the Tortoise. _j_, Joints of the backbone grown together; _r_, ribs formed into a solid cover; _sh_, shoulder bones; _h_, hip bones covered by carapace, which has grown over them. ]