Locomotion. Locomotion is performed by pulling and pushing the body along the ground, a leverage being obtained by means of the broad flat scales, or scutes, with which the ventral side of the body is covered. Snakes can also move without twisting the body. This is accomplished by a regular drawing forward of the scutes (with the ribs under them) and then pushing them backward rather more violently.

Feeding Habits.

The bones of the jaw are very loosely joined together. Thus the mouth of the snake is capable of wide distention. It holds its prey by means of incurved teeth, two of which (in the poisonous snakes) are hollow, and serve as a duct for the passage of poison. The

poison glands are found
at the base of the curved
fangs in the upper jaw.
The tongue is very long
and cleft at the end. It
is an organ of touch and
taste, and is not, as many
people believe, used to
sting with. The food is
swallowed whole, after
having been caught by
the teeth, and pushed
down by rhythmic contractions of the muscles surrounding the
gullet. They refuse other than living prey. After a full meal,
one of which is sufficient for weeks, the snake remains in a torpid
condition.

Skull of boa constrictor, two thirds natural size.
From photograph by Davison.

Adaptations. The extreme length of the body in the snake has resulted in the modification of the form of its internal organs. One long, narrow lung is developed instead of two. The glands of the body cavity are long and slender, while the kidneys are placed so that one is anterior to the other.

Snakes are usually colored to harmonize with their surroundings. Thus they may approach and seize their prey before it escapes. They are not extremely prolific animals, but hold their own with other forms of life, because of their numerous adaptations HUNTER'S BIOL.- - 19

for protection, their noiseless movement, protective color, and, in some cases, by their odor and poison.

Poisonous Snakes. Not all snakes can be said to be harmless. The bite of the rattlesnake of our own country, although dangerous, seldom kills. The dreaded cobra of India has a record of over two hundred and fifty thousand persons killed in the last thirty-five years. The Indian government yearly pays out large sums for the extermination of venomous snakes, over two hundred thousand of which have been killed during a single year.

Alligators and Crocodiles. The latter are mostly confined to Asia and Africa, while the former are natives of this continent and

South America. The chief structural difference between them is that the teeth in alligators are set in long sockets, while those of the crocodile are not. Both of these great lizardlike animals have broad, flattened tails adapted to swimming. The eyes and nostril holes protrude from the head, so that the animal may float motionless near the surface of the water with only eyes and nostrils visible. The nostrils are closed by a valve when the animal is under water. They feed on fishes, but are known to attack large animals, as horses, cows, and even man. They seek their prey chiefly at night; and spend the day basking in the sun. The crocodiles of the Ganges River in India levy a yearly tribute of many hundred lives from the natives.

CLASSIFICATION OF REPTILES

ORDER I. Chelonia (turtles and tortoises).

Flattened reptiles with body enclosed in bony case. No teeth or sternum (breast bone). Examples, snapping turtle, box tortoise.

ORDER II. Lacertilia (lizards). Body covered with scales, usually having twopaired appendages. Breathe by lungs. Example, fence lizard, horned toad. ORDER III. Ophidia (snakes). Body elongated, covered with scales. No limbs present. Examples, garter snake, rattlesnake.

ORDER IV. Crocodilia. Freshwater reptiles with elongated body and bony scales on skin. Two paired limbs. Examples, alligator, crocodile.

REFERENCE BOOKS

FOR THE PUPIL

Davison, Practical Zoology, pages 211-226. American Book Company.
Herrick, Text-book in General Zoology, Chap. XXI. American Book Company.
Jordan, Kellogg, and Heath, Animal Studies, Chap. XVI. D. Appleton and
Company.

FOR THE TEACHER

Riverside Natural History. Houghton, Mifflin, and Company.

Parker and Haswell, Text-book of Zoology. The Macmillan Company.

XXV. BIRDS

THE following questions may be worked out during a visit to a zoological park or during a field trip.

Pick out some particular bird for your study and take notes upon the following series of questions. Do not expect to be able to answer all the questions which follow.

Protection. Does the bird rest or nest in trees, bushes, or grass? In general, what are the colors of the bird? Do they harmonize with the surroundings when the bird is at rest? Look especially for birds on the nest. Often such birds will remain quiet, allowing the observer almost to touch

them before they attempt to fly away. In some cases the light, glinting through the trees, gives a mottled or banded appearance to the leaves, somewhat resembling the same kind of markings on a bird.

Flight. Watch a bird in flight. Try to determine the exact changes in the position of the wings that take place. The tip of the wing usually describes a curve which results in the forming of the figure. Notice that the rate of movement of the wing differs greatly in different birds. Birds with

long, thin wings, as the hawks and gulls, move the wing in flight with much less rapidity than those with short, wide wings, as the grouse or quail. The latter birds start with much less apparent effort than the birds with longer wings; they are, however, less capable of sustained flight.

The wing of a bird is slightly concave on the lower surface when outstretched. Thus on the downward stroke of the wing more resistance is offered to the air.

Under the covering of feathers the parts of the wing may be made out. This may easily be done from a fowl at home, or dead sparrows may be used in the laboratory. Find and identify the parts corresponding to the human arm, forearm, and hand. The last division of the wing is homologous to our

1 Bird activities may best be studied out of doors. Any city park offers more or less opportunity for such study, for several of our native birds make the parks their home. If not these, then the English sparrow can be found anywhere in the East. The best time for making observations is early in the morning, especially in the Spring season.

hand and wrist, the third and fourth fingers are absent while the wrist bones and fingers of the fowl have grown together, thus giving greater strength and support. This is evidently an adaptation for flight.

Feathers. Few people realize that the body of a bird is not completely covered with feathers. Look for featherless areas on the body of the bird you are working with. Notice that feathers are of several shapes. Soft down feathers cover the body, serving for bodily warmth. In the wings we find quill feathers; these are adapted for service in flight. Let us examine a single quill feather more closely. The main axis of the feather, called the shaft, is hollow, light, and strong. From the shaft, lateral branches, called barbs, are given off. The barbs give rise to still smaller lateral structures, the barbules, the latter just visible to the naked eye. Each barbule is interlocked with its neighbor by means of many microscopic hooks, the barbicels. If you attempt to pull apart the barbs of a feather, you will find that they stick together. What is the reason for this? Might this arrangement be of use in flight, and if so, how?

Draw a quill feather and show all the parts visible to the naked eye.

Feathers. Feathers are developed from the under layer of the skin. At first they appear to be tiny, pimplelike projections. They are formed in almost exactly the same manner as are the scales of a fish or a lizard. The first feathers developed on the body are evidently for protection against cold and wet. In aquatic birds the feathers are oiled constantly, and thus shed water. The feathers of some male birds are brightly colored. This seems to make them attractive to the females of the species; thus the male wins its mate.

Perching. The habit of perching is an interesting one. In many perching birds the tendons of the leg and foot, which regulate the toes, are self locking; thus while asleep such birds balance themselves perfectly. A certain part of the ear, known as the semicircular anals, has to do with the function of balancing. In the flamingoes, which do not perch, balancing appears to be automatic and elf-regulating; thus the bird is able to go to sleep when in an upright position.

Tail. The tail is sometimes used in balancing; its chief function, however, appears to be that of a rudder during flight. Note that the tail is merely a small protuberance of the body, the feathers which grow there give it the shape. In most birds, under the skin of the tail is located a large oil gland, whence comes the supply of oil that is used in waterproofing the feathers.

Adaptation in the Lower Limbs. In the leg identify the thigh, the shin, and foot. The ankle of the bird is extremely long, the seven bones found