CHAPTER XII

REPTILIA (REPTILES)

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.

[Illustration: FIG. 263.--A SALAMANDER.]

[Illustration: FIG. 264.--A LIZARD.]

=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).

[Illustration: FIG. 265.--“HORNED TOAD” LIZARD, of the Southwest (_Phrynosoma cornita_). × ²⁄₃.]

STUDY OF A TURTLE OR TORTOISE

SUGGESTIONS.--Because of the ease with which a tortoise or turtle may be caught and their movements and habits studied, it is suggested that one of these be studied as an example of reptiles. Besides a live specimen, a skeleton of one species and the shells of several species should be available.

[Illustration: FIG. 266.--EUROPEAN POND TURTLE (_Emys lutaria_). (After Brehms.)]

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.)

[Illustration: FIG. 267.--SKELETON OF EUROPEAN TORTOISE.

_C_, rib plates; _M_, marginal plates; _B_, plastron; _H_, humerus bone; _R_, radius; _U_, ulna; _Fe_, femur.]

[Illustration: FIG. 268.--THREE-CHAMBERED HEART OF A REPTILE (tortoise).

_a_, veins; _b_, _f_, right and left auricles; _cg_, ventricle; _d_, arteries to lungs; e, veins from lungs; _i_, _n_, two branches of aorta. Compare with Fig. 269 and colored Fig. 2.]

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.

[Illustration: FIG. 269.--PLAN OF REPTILIAN CIRCULATION. See arrows.]

=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.

[Illustration: FIG. 270.--REPTILIAN VISCERA (lizard).

_lr_, windpipe; _h_, heart; _lu_, lungs; _le_, liver; _ma_, stomach; _dd_, _md_, intestines; _hb_, bladder.]

=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.

[Illustration: FIG. 271.--SNAPPING TURTLE (_Chelydra serpentina_).]

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.

[Illustration: FIG. 272.--A RATTLESNAKE.]

[Illustration: FIG. 273 _a_.--HEAD OF VIPER, showing typical triangular shape of head of venomous snake.]

[Illustration: FIG. 273 _b_.--SIDE VIEW, showing poison fangs; also tongue (forked, harmless).]

[Illustration: FIG. 274.--VIPER’S HEAD, showing poison sac at base of fangs.]

[Illustration: FIG. 275.--SKULL, showing teeth, fangs, and quadrate bone to which lower jaw is joined. See Fig. 284].

=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.

[Illustration: FIG. 276.--“GLASS SNAKE,” a lizard without legs.]

[Illustration: FIG. 277.--SKULL OF ELAPS. See colored Fig. 5.]

[Illustration: FIG. 278.--SKULL OF LAMPROPELTIS.]

=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 coloration_or _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.

[Illustration: FIG. 1

FIG. 2

FIG 3.

COLORED FIGURES 1, 2, 3.--CIRCULATION IN FISH, REPTILE, MAMMAL.

In which is blood from heart all impure? Mixed? Both pure and impure?]

[Illustration: FIG. 4.--ANATOMY OF CARP. For description see Fig. 220, page 117.]

[Illustration: THE HARMLESS CORAL SNAKE MIMICS THE DEADLY HARLEQUIN SNAKE.

FIG. 5.--HARLEQUIN SNAKE (_Elaps_).

FIG. 6.--CORAL SNAKE (_Lampropeltis_).]

[Illustration: FIG. 279.--GILA MONSTER (_Heloderma suspectum_), of Arizona. If poisonous, it is the only instance among lizards. It is heavy-built, orange and black mottled, and about 16 inches long. Compare it with the green lizard (Fig. 280).]

[Illustration: FIG. 280.--CHAMELEON (_Anolis_), or green lizard of southern U.S. Far excels European chameleon (Fig. 281) and all known animals in power of changing color (green, gray, yellow, bronze, and black).]

=Survival of the Fittest=.--The two facts of most far-reaching importance in the history of animals and plants are: (1) _Heredity_; animals inherit the characteristics of their parents. (2) _Variation_; animals are not exactly like their parents. The first fact gives stability, the second makes progress or evolution possible. The climate of the world is slowly changing, and animals must change to adapt themselves to it. A more sudden change of environment (surroundings) of animals occurs because of migration or isolation; these in turn are caused by the crowding of other animals or by the formation or disappearance of geographical barriers, such as deserts, water, mountain chains.

[Illustration: FIG. 281.--CHAMELEON OF SOUTHERN EUROPE.]

The young vary in many ways from their parents. Some have a more protective color or form, sharper claws, swifter movements, etc. The individuals possessing such beneficial variations live longer and leave more offspring, and because of heredity transmit the desirable qualities to some of their young. Variations which are disadvantageous for getting food, defense, etc., cause shorter life and fewer offspring. Thus the _fittest survive_, the unfit perish; an automatic _natural selection_ occurs.

Darwin taught that variations are infinitesimal and gradual. Recent experiments and observations seem to show that many variations are by sudden jumps, somewhat resembling so-called “freaks of nature.” As to whether these “sports,” or individuals with new peculiarities, survive, depends upon their fitness for their environment. “Survival of the fittest” results from this natural selection, but the selection occurs between animals of marked, not infinitesimal, differences, as Darwin taught. Darwin’s theory is probably true for species in the usual state of nature; the new theory (of De Vries) is probably true for animals and plants under domestication and during rapid geographical changes.

[Illustration: FIG. 282.--EMBRYO OF A TURTLE, showing four gill slits. (Challenger Report.)]

=Table for Review= (for notebooks or blackboards).

========================+========+========+========+========+======== | FISH | TADPOLE| FROG | TURTLE | LIZARD ------------------------+--------+--------+--------+--------+-------- | | | | | Limbs, kind and number | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Are claws present? How | | | | | many? | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Covering of body | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Teeth, kind of, if | | | | | present | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Which bones found in man| | | | | are lacking? | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Chambers of heart | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Respiration | | | | | | | | | | ------------------------+--------+--------+--------+--------+-------- | | | | | Movements | | | | | | | | | | ========================+========+========+========+========+========

[Illustration: FIG. 283.--BIG-HEADED TURTLE (_Platysternum megalocephalum_). × ¹⁄₂. China. This and Fig. 282 suggest descent of turtles from a lizardlike form. Figure 282 shows earlier ancestors to have been gill breathers.]