thickness. Many of the sea-water turtles are of large size, the leatherback and the green turtle often weighing six hundred to The flesh of the green turtle and

seven hundred pounds each.

especially the diamond

back terrapin, an animal

found in the salt marshes along our southeastern coast, are highly esteemed as food. Unfortunately for the preservation of the species, these animals are usually taken during the breeding season, when they go to sandy beaches to lay their eggs. Characteristics of the Reptilia. The turtle belongs to the class of vertebrates known as the Reptilia. These animals are characterized by having scales developed from the skin. These in the turtle have become bony and are connected with the internal skeleton. Turtles always breathe by means of lungs, differing in this respect from the amphibians. They seem to show their distant relationship to birds in that their eggs are large and are encased in a leathery, limy shell.

Box tortoise (Terrapin). From photograph loaned by the American Museum of Natural History.

Lizards. Lizards may be recognized by the long body with four legs of nearly equal size. The body is covered with scales. The animal never lives in water, it is active in habit, and it does not undergo a metamorphosis. Salamanders (commonly called lizards) have a moist skin, and belong to the Amphibia. Lizards are harmless creatures, the Gila monster of New Mexico and Arizona, a poisonous variety, being the one exception. Lizards are, on the whole, of economic importance to man because they eat insects and include the injurious ones in their dietary. Certain lizards, including injurious ones, notably the chameleon and our common fence lizard, have the power to change the color of the skin. This forms a protective adaptation, for they thus assume the color of their immediate surroundings. The horned toad of our Western states shows another wonderful case of protective adap

Horned toad. Note the protective resemblance.

tation. The iguana of Central America and South America is among the largest of lizards, growing to a length of three feet or more. It has the distinction of being one of the few edible lizards. Snakes. Probably the most disliked and feared of all animals are the snakes. This feeling, however, is rarely deserved. Our common snakes are harmless and were it not for the fact that they live upon insect-destroying animals, as toads, frogs, and birds, we might even say that they are useful to man.

Snakes are almost the only legless vertebrates. Although the limbs are absent, still the pelvic and pectoral girdles are developed. The very long backbone is made up of a large number of vertebræ, as many as four hundred Ribs are attached to all ver

Rattlesnake three feet long coiled ready to strike. In this position it can dart its head forward two feet only. From photograph by Davison.

being found in the boa constrictor. tebræ in the region of the body cavity.

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.

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.