compare with the fish and the frog; the head, its shape and various parts composing it, the jaws, eyes, nostrils; note the absence of teeth; the tongue.

Remove the lower half of the shell and study the internal organs composing the digestive, circulatory, reproductive, and excretory systems; compare the structure of the heart with that of the fish and the frog (Fig. 273).

On a skeleton note the various parts which are attached to the shell; the skull and neck; the hyoid apparatus, the structure of the limbs and tail; compare the hyoid apparatus and the ribs with those of the frog (Fig. 312).

If eggs can be obtained, note the shape, structure of the shell, and the stages of development of the young.

Bird

Sparrows or pigeons may be used.

Field Study. Note its general mode of life, whether solitary or gregarious; relations to other birds and to man; its manner of flight and of walking; feeding habits; size, shape, and coloration of the body; variations in coloration at different seasons of the year; position and structure of the nest, number, shape, size, and color of eggs, number of broods each year, season when broods are produced, and number of young in each brood; enemies; song; if a living specimen can be obtained, test the body temperature with a ther

mometer.

Structure. With a recently killed specimen, study the shape of the body, the direction of its axis; the position and mobility of the head, wings, legs, and tail; the distribution of the various feathers, their structure (Figs. 139, 302). Remove the latter and note the feather tracts and the skin. Study the shape and structure of

the head, the beak, eyes, nostrils, and ears; compare with the turtle. Examine the wings and legs, noting the direction and movements of the various segments; the structure and movements of the parts of the foot; the position of the principal muscles, their uses.

Open the body and study the digestive, circulatory, respiratory, and reproductive systems (Figs. 248, 273); the air spaces among the muscles; the structure of the heart and brain as compared with the vertebrates previously studied (Fig. 338); the microscopic appearance of the blood corpuscles (Fig. 262).

Prepare or purchase a skeleton and study the arrangement of its various parts and the structure of the different bones, comparing with the fish, frog, and turtle (Fig. 313).

Study the structure of the egg (Fig. 358), and the development of the young (a convenient and satisfactory substitute is the hen's egg) (Figs. 365, 366). Draw attention to the economic value of the bird studied.

Mammal

The cat or rabbit may be used.

Laboratory Study.-Study the motions of the animal as it walks, runs, leaps, its position when at rest; food and mode of feeding; respiratory movements; motions of head, legs, tail, ears, eyes; mode of cleaning its fur; body temperature; protective coloration.

Structure. — On a recently killed specimen note the general shape of the body and direction of its axis; the position and mode of attachment of the appendages; the hairy covering, the groups of specialized hairs in certain positions, the microscopic appearance of hair; the mobility of the skin; its firmer attachment in certain places, compare with the external covering of fish, frog, turtle, and bird. Study the shape and structure

of the head, the position and structure of ears, eyes, nostrils, and mouth.

Remove the skin from the body and study the position and attachment of the more important muscles, their uses. Open the body and examine the organs composing the digestive, circulatory, respiratory (Fig. 283), excretory, and reproductive systems (Fig. 250). Note the posi

tion and structure of the teeth and their fitness to masticate the special kind of food the animal eats; the surface of the tongue and its adaptation as an organ for cleaning the fur; compare the heart and brain (Fig. 339), and the microscopic appearance of the blood corpuscles with those of other vertebrates examined (Fig. 259).

Trace the course of some of the principal blood vessels and nerves.

Examine a skeleton and compare with that of the other vertebrates studied (Fig. 303).

A series of preparations of fetal kittens or rabbits may be examined.

CHAPTER II

THE CLASSIFICATION OF ANIMALS

THE Kingdom of Nature is a literal Kingdom. Order and beauty, law and dependence, are seen everywhere. Amidst the great diversity of the forms of life, there is unity; and this suggests that there is one general plan, but carried out in a variety of ways.

Naturalists have ceased to believe that each animal or group is a distinct, circumscribed idea. "Every animal has a something in common with all its fellows: much with many of them; more with a few; and, usually, so much with several, that it differs but little from them." The object of classification is to bring together the like, and to separate the unlike. But how shall this be done? To arrange a library in alphabetical order, or according to size, binding, date, or language, would be unsatisfactory. We must be guided by some essential character. We must decide whether a book is poetry or prose; if poetry, whether dramatic, epic, lyric, or satiric; if prose, whether history, philosophy, theology, philology, science, fiction, or essay. The more we subdivide these groups, the more difficult the analysis.

A classification of animals, founded on external resemblances as size, color, or adaptation to similar habits of life-would be worthless. It would bring together fishes and whales, birds and bats, worms and eels. Nor should it be based on any one character, as the quality of the blood, structure of the heart, development of the brain, embryo life, etc.; for no character is

of the same value in every tribe. A natural classification must rest on those prevailing characters which are the most constant. And such a classification can not be linear. It is impossible to arrange all animal forms from the sponge to man in a single line, like the steps of a ladder, according to rank. Nature passes in so many ways from one type to another, and so multiplied are the relations between animals, that one series is out of the question. There is a number of series, and series within series, sometimes proceeding in parallel lines, but more often divergent. The animals arrange themselves in radiating groups, each group being connected, not with two groups merely, one above and the other below, but with several. Life has been likened to a great tree with countless branches spreading widely from a common trunk, and deriving their origin from a common root; branches bearing all manner of flowers, every fashion of leaves, and all kinds of fruit, and these for every use.

The groups into which we are able to cast the various forms of animal development are very unequal and dissimilar. We must remember that a genus, order, or class is not of the same value throughout the kingdom. Moreover, each division is allied to others in different degrees the distance between any two being the measure of that affinity. The lines between some are sharp and clear, between others indefinite. Like the islands of an archipelago, some groups merge into one another through connecting reefs, others are sharply separated by unfathomable seas, yet all have one common basis. Links have been found revealing a relationship, near or distant, even between animals whose forms are very unlike. There are fishes (Dipnoi) with some amphibian characters, and fishlike amphibians (Axolotl). The extinct ichthyosaurus was a lizard with fish charac