Into the space within this shell most tortoises may withdraw the head and tail which, like the feet, are covered with horny scales. The head has good eyes, and a nose with a lively sense of smell, which the creature utilizes in selecting its food; but its hearing appears to be dull. The mouth has no teeth, but the lips are coated with horn, making a parrotlike beak that can inflict a severe bite. Horny spines often grow on the legs, or tail, or both, assisting in both defense and offense.
The chelonians are a very ancient race, and one that has changed remarkably little since its beginning. The great age accounts for the very wide distribution of turtles closely related, and also for the fact that they inhabit land, fresh and salt water; those of the land being, no doubt, the oldest. All turtles lay eggs, the shell of which varies, according to kind, from a parchmentlike envelope to a hard, shining shell; but the process of generation is slow and curiously complicated.
The respiration of the Chelonia is interesting. The lungs are spongy masses, attached to the upper shell. As the rigid case does not permit of their expansion by breathing, the necessary vacuum is made partly by the neck and limbs, which act like pistons as they are drawn in and out, the air being swallowed or pumped into the lungs. Most chelonians may exist for a very long time without breathing, and can stay for hours or even days under water. No animal, perhaps, is harder to kill; and all turtles have long lives, the giant turtles of the Galapagos and their kin living more than 100 years.
The list of Thecophora begins with the suborder Cryptodira, whose members have the carapace covered with horny shields, and consists of the family Chelydridæ, composed of our two snapping turtles, the familiar northern one, and the southern alligator snapper. They inhabit stagnant pools, especially deep channels in swamps and slow rivers such as the bayous of the lower Mississippi Valley, and often show only the tip of the nose as they prowl about close beneath the surface in search of prey—anything they can seize. They take the hook readily if baited with fish or flesh, but stout tackle and a strong arm are needed to land one when full grown; and the act is dangerous to the catcher, for they are the ugliest brutes in the country, and to be bitten by one is a very serious experience. Nevertheless, the young are caught for market in large numbers, for they are excellent food. One curious fact about them is not generally known, namely, that when lying still, like a piece of old log covered with mud and moss, they protrude a pair of wormlike filaments from the tip of the tongue, whose wavering attracts fishes to their doom. Louis Agassiz says of the great alligator snapper of the Southern States, which when walking on land carries its body high on the long legs, much like an alligator:
"They are as ferocious as the wildest beast of prey, but the slowness of their motions, their inability to repeat the attack immediately, their awkwardness in attempting to recover their balance when they have missed their object, their haggard look, and the hideous appearance of their gaping mouth, constitute at such times a picture as ludicrous as it is fearful and revolting. Their strength is truly wonderful. I have seen a large specimen bite off a piece of plank more than an inch thick.... Fishes, salamanders and young ducks are their ordinary prey. They lay from twenty to forty or more round eggs, only about the size of a small walnut, in holes which they dig in sloping banks not far from the water."
These snapping turtles probably represent well the disposition and habits of the extinct predatory reptiles; and give us a hint of why the race succumbed to the more active and intelligent mammals that were growing up around them toward the close of the Mesozoic.
This brings us to the great family Testudinidæ, which is scattered over the whole world except Australia, and contains almost all the ordinary tortoises, mud turtles and terrapins, some of which are entirely aquatic, others amphibious, others wholly terrestrial. Among the most typical and widely distributed are those of the genus Chrysemys, to which "mud turtles" belong. The commonest species in the Eastern States is the painted turtle Chrysemys picta; in the West, C. marginata. These and other species of North and South America are very pretty when young, the ground color of the upper shields being green, variegated with yellowish or blackish markings, often in delicate patterns. They are carnivorous, depend mainly on fish, but eat many insects and their larvæ. In winter they hibernate in holes in a bank of their pond.
| TERRAPIN |
| (Malaclemys palustris) (After Babcock. Boston Society of Natural History) |
To the genus Clemmys is credited the "sculptured" wood tortoise, the keeled plates of whose back are marked with fine concentric grooves and radiating black lines; and the equally common speckled one, black with round, orange spots. Both spend long periods wandering in woods and fields in search of worms and insects. Closely related to them are the salt-marsh tortoises known as terrapins, which are so much of a luxury in the eyes of those fond of good dinners that probably the favorite one, the "diamond back," would be extinct had not protective measures, and cultivation in captivity, saved the life of the species. Several other terrapins are to be found in the marshes of the Southern States, but not in other countries. Another relative is the interesting little "box tortoise," which is often kept as a pet, and will become very tame; its highly convex shell is colored black and yellow, or orange-brown, but no two are alike. The eyes of the male are red, those of the female yellow. It is naturally enough a "box" tortoise, for, by means of a flexible joint line across the plastron, the fore and hinder halves can be brought up to the ends of the carapace, shutting the whole body inside a tight box that will defy all enemies not strong enough—as are wolves, bears, and big cats—to tear it to pieces. This tortoise is exclusively American. It has become, as a species, wholly terrestrial, so much so that, although it is fond of drinking often, if it falls into the water it will drown. It thus leads us to the true land tortoises that fill the remaining genera of this family.