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_). × ⅔.
]
STUDY OF A TURTLE OR A TORTOISE
SUGGESTIONS.—Because of the ease with which a tortoise or a 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 a 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
the 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 the 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 a 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 =colours= of turtles? How does their colouration
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?
[Illustration:
FIG. 267.—SKELETON OF EUROPEAN TORTOISE.
_C_, rib plates; _M_, marginal plates; _B_, plastron; _H_, humerus
bone; _R_, radius; _U_, ulna; _Fe_, femur.
]
=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 collarbones? Hipbones? Thigh
bones? Shin bone (fibia) and splint bone (fibula)? (Fig. 267.)
[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 coloured 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.
[Illustration:
FIG. 270.—REPTILIAN VISCERA (lizard).
_lr_, windpipe; _h_, heart; _lu_, lungs; _lr_, liver; _ma_, stomach;
_dd_, _md_, intestines; _hb_, bladder.
]
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.
[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.
]
=Venomous snakes= named in order of virulence: 1. Coral snakes, _Elaps_,
about seventeen red bands bordered with yellow and black (coloured
figure 6) (fatal). 2. Rattlesnakes (very deadly). 3. Copperhead (may
kill a small animal of the size of a 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. No one but a physician should give strychnine.
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 colour
or form of its _inanimate surroundings_ it is said to be _protectively
coloured_ or formed. Give an instance of _protective Coloration_ or
_form_ among lizards; butterflies; grasshoppers; amphibians;
echinoderms. When an animal imitates the colour or the 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 most
deadly snake of North America (Figs. 277, 278). It is very strikingly
coloured with rings of scarlet, yellow, and black. This is an example of
_warning_ coloration. The scarlet snake (_Lampropeltis_) has bands of
scarlet, yellow, and black (coloured Fig. 6) of the same tints, and it
is hardly distinguishable from the harlequin. The scarlet 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 but
deadly 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:
COLOURED 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.
]
THE DEADLY HARLEQUIN SNAKE IS MIMICKED BY THE HARMLESS SCARLET SNAKE.
[Illustration:
FIG. 5.—HARLEQUIN SNAKE (_Elaps_).
]
[Illustration:
FIG. 6.—SCARLET 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 colour (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 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 colour 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, defence, etc., cause shorter life and fewer
offspring. Thus the _fittest survive_, the unfit perish; an automatic
_natural selection_ occurs.
[Illustration:
FIG. 282.—EMBRYO OF A TURTLE, showing four gill slits. (Challenger
Report.)
]
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.
=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_). × ⅓.
China.
This and Fig. 282 suggest descent of turtles from a lizardlike form.
Figure 282 shows earlier ancestors to have been gill breathers.
]