This class is divided into four orders which have such marked differences of external form that there is no difficulty in distinguishing them. These orders are represented by Lizards, Snakes, Turtles, and Alligators. Of these, only the forms of lizards and alligators have similar proportions, but there is a marked difference in their size, lizards being, in general, the smallest, and alligators the largest of the reptiles.

Comparison of Lizards and Salamanders.—To make clear the difference between reptiles and batrachians, it will be well to compare the orders in the two classes which resemble each other in size and shape; namely, lizards and salamanders (Figs. 263 and 264). State in a tabular form their differences in skin, toe, manner of breathing, development from egg, shape of tail, habitat, habits. Each has an elongated body, two pairs of limbs, and a long tail, yet they are easily distinguished. Are the differences suggested above valid for the other batrachians (frogs) and other reptiles (e.g. turtles)? Trace the same differences between the toad or frog (Fig. 250) and the “horned toad,” which is a lizard (Fig. 265).

Study of a Turtle or Tortoise

The body (of a turtle or tortoise) is divided distinctly into regions (Fig. 266). Is there a head? Neck? Trunk? Tail? The trunk is inclosed by the so-called shell, which consists of an upper portion, the carapace, and a lower portion, the plastron. How are the other regions covered? What is the shape of the head? Is the mouth at the front, or on the under side? Where are the nostrils? Are the motions of breathing visible? Is there a beak or snout? Do the jaws contain teeth?

Do the eyes project? Which is thinner and more movable, the upper or lower lid? Identify the third eyelid (nictitating membrane). It is translucent and comes from, and is drawn into, the inner corner of the eye. It cleanses the eyeball. Frogs and birds have a similar membrane. The circular ear drum is in a depression back of the angle of the mouth. What other animal studied has an external ear drum?

The tortoise has a longer, more flexible neck than any other reptile. Why does it have the greatest need for such a neck? Is the skin over the neck tight or loose? Why?

Do the legs have the three joints or parts found on the limbs of most vertebrates? How is the skin of the legs covered? Do the toes have claws? Compare the front and hind feet. Does the tortoise slide its body or lift it when walking on hard ground? Lay the animal on its back on a chair or table at one side of the room in view of the class. Watch its attempts to right itself. Are the motions suited to accomplish the object? Does the tortoise succeed?

What are the prevailing colors of turtles? How does their coloration correspond to their surroundings?

What parts of the tortoise extend at times beyond the shell? Are any of these parts visible when the shell is closed? What movements of the shell take place as it is closed? Is the carapace rigid throughout? Is the plastron?

The Skeleton (Fig. 267).—The carapace is covered with thin epidermal plates which belong to the skin. The bony nature of the carapace is seen when the plates are removed, or if its inner surface is viewed (Fig. 267). It is seen to consist largely of wide ribs (how many?) much flattened and grown together at their edges. The ribs are seen to be rigidly attached to the vertebræ. The rear projections of the vertebræ are flattened into a series of bony plates which take the place of the sharp ridge found along the backs of most vertebrates. Show that the shell of a turtle is not homologous with the shells of mollusks. Does the turtle have shoulder blades and collar bones? Hip bones? Thigh bones? Shin bone (fibia) and splint bone (fibula)? (Fig. 267.)

Do the plates formed by the ribs extend to the edge of the carapace? See Fig. 267. About how many bony plates form the carapace? The plastron? Do the horny plates outside correspond to the bony plates of the shell? How many axial plates? How many costal (rib) plates? How many border plates? Which plates are largest? Smallest? Do the horny plates overlap like shingles, or meet edge to edge? Is there any mark where they meet on the bony shell? Basing it upon foregoing facts, give a connected and complete description of the structure of the carapace. Compare the skeleton of the turtle with that of the snake, and correlate the differences in structure with differences in habits.

Draw the tortoise seen from the side or above, with its shell closed, showing the arrangement of the plates.

Place soft or tender vegetable food, lettuce, mushroom, roots, berries, and water, also meat, in reach of the turtle. What does it prefer? How does it eat? It has no lips; how does it drink?

Study the movements of its eyeballs and eyelids, and the respiratory and other movements already mentioned. State a reason for thinking that no species of land animals exists that lacks the simple power of righting itself when turned on its back.

Tortoise, Turtle, Terrapin.—The turtles belong to the order of reptiles called chelonians. No one can have any difficulty in knowing a member of this order. The subdivision of the order into families is not so easy, however, and the popular attempts to classify chelonians as turtles, tortoises, and terrapins have not been entirely successful. Species with a vaulted shell and imperfectly webbed toes and strictly terrestrial habits are called tortoises. Species with flattened shells and strictly aquatic habits should be called terrapins (e.g. mud terrapin). They have three instead of two joints in the middle toe of each foot. The term turtle may be applied to species which are partly terrestrial and partly aquatic (e.g. snapping turtle (Fig. 271)). Usage, however, is by no means uniform.

Most reptiles eat animal food; green terrapins and some land tortoises eat vegetable food. Would you judge that carnivorous chelonians catch very active prey?

The fierce snapping turtle, found in ponds and streams, sometimes has a body three feet long. Its head and tail are very large and cannot be withdrawn into the shell. It is carnivorous and has great strength of jaw. It has been known to snap a large stick in two. The box tortoise is yellowish brown with blotches of yellow, and like its close kinsman, the pond turtle of Europe (Fig. 266), withdraws itself and closes its shell completely. Both lids of the plastron are movable, a peculiarity belonging to these two species. The giant tortoise of the Galapagos Islands, according to Lyddeker, can trot cheerfully along with three full-grown men on its back. “Tortoise shell” used for combs and other articles is obtained from the overlapping scales of the hawkbill turtle, common in the West Indies. The diamond-back terrapin, found along the Atlantic Coast from Massachusetts to Texas, is prized for making soup.

Poisonous snakes of United States named in order of virulence: 1. Coral snakes, Elaps, about seventeen red bands bordered with yellow and black (colored figure 6) (fatal). 2. Rattlesnakes (seldom fatal). 3. Copperhead (may kill a small animal size of dog). 4. Water moccasin (never fatal). 5. Ground rattler.—Effects: Pulse fast, breathing slow, blood tubes dilated, blood becomes stored in abdominal blood tubes, stupefaction and death from blood being withdrawn from brain. Always two punctures, the closer together the smaller the snake. Remedies: Ligature between wound and heart, lance wound and suck; inject into wound three drops of 1 per cent solution of chromic acid or potassium permanganate. Give strychnine, hypodermically, until strychnine symptoms (twitchings) appear. If symptoms of collapse recur, repeat dose. Digitalin or caffein acts like strychnine; alcohol has opposite effect.

Protective Coloration and Mimicry.—When an animal imitates the color or form of its inanimate surroundings it is said to be protectively colored or formed. Give an instance of protective colorationor form among lizards; butterflies; grasshoppers; amphibians; echinoderms. When an animal imitates the color or form of another animal it is said to mimic the animal. Mimicry usually enables an animal to deceive enemies into mistaking it for an animal which for some reason they avoid. The milkweed butterfly has a taste that is repulsive to birds. The viceroy butterfly is palatable to birds, but it is left untouched because of its close resemblance to the repulsive milkweed butterfly. The harlequin snake (Elaps) of the Gulf states is the only deadly snake of North America (Figs. 277, 278). It is very strikingly colored with rings of scarlet, yellow, and black. This is an example of warning coloration. The coral snake (Lampropeltis) has bands of scarlet, yellow, and black (colored Fig. 6) of the same tints, and it is hardly distinguishable from the harlequin. The coral snake is said to mimic the harlequin snake. It also imitates the quiet inoffensive habits of the harlequin snake, which fortunately does not strike except under the greatest provocation. The rattles of the less poisonous and seldom fatal rattlesnake (Fig. 272) may be classed as an example of warning sound which most animals are quick to heed and thus avoid encounters which might be destructive to either the snake or its enemy.

Table for Review (for notebooks or blackboards).