Part 14

III. Coelenterates.--The hydra and its salt-water allies, the jellyfish, hydroids, and corals, belong to a group of animals known as the _Coelenterata_. The word "coelenterate" (_coelom_ = body cavity, _enteron_ = food tube) explains the structure of the group. They are animals in which the real body cavity is lacking, the animal in its simplest form being little more than a bag. Some examples are the hydra, shown on page 179, salt-water forms known as hydroids, colonial forms which have part of their life free swimming as jellyfish; sea anemones and coral polyps, tiny colonial hydra like forms which build a living or secreted covering.

IV. Worms.--The wormlike animals are grouped into _flatworms_, _roundworms_, and segmented or _jointed_ worms.

(_a_) Flatworms are sometimes parasitic, examples being the tapeworm and liver fluke. They are usually small, ribbon- or leaf-like and flat and live in water.

(_b_) Roundworms, minute threadlike creatures, are not often seen by the city girl or boy. Vinegar eels, the horsehair worm, the pork worm or trichina and the dread hookworm are examples.

(_c_) Segmented worms are long, jointed creatures composed of body rings or segments. Examples are the earthworm, the sandworm (known to New York boys as the fishworm), and the leeches or bloodsuckers.

V. Echinoderms.--These are spiny-skinned animals, which live in salt water. They are still more complicated in structure than the worms and may be known by the spines in their skin. They show radial symmetry. Starfish or sea urchins are examples.

VI. Arthropods.--These animals are distinguished by having jointed body and legs. They form two great groups. The higher forms of the _Crustacea_ have only two regions in the body, a fused head and thorax, called the _cephalothorax_, and an abdominal region. A second group is the _Insecta_, of which we know something already. Crustacea breathe by means of _gills_, which are structures for taking oxygen out of the water, while adult insects breathe through air tubes called _trachea_.

Two smaller groups of arthropods also exist, the _Arachnida_, consisting of spiders, scorpions, ticks, and mites, and the _Myriapoda_, examples being the "thousand leggers" found in some city houses.

VII. Mollusca.--Another large group is the Mollusca. This phylum gets its name from the soft, unsegmented body (_mollis_ = soft). Mollusks usually have a shell, which may be of one piece, as a snail, or two pieces or _valves_, as the clam or oyster.

VIII. The Vertebrates.--All of the animals we have studied thus far agree in having whatever skeleton or hard parts they possess on the outside of the body. Collectively, they are called _Invertebrates_. This exoskeleton differs from the main or axial skeleton of the higher animals, the latter being inside of the body. The exoskeleton is dead, being secreted by the cells lining the body, while the endoskeleton is, in part at least, alive and is capable of growth, _e.g._ a broken arm or leg bone will grow together. But a man has certain parts of the skeleton, as nails or hair, formed by the skin and in addition possesses inside bones to which the muscles are attached. Some of the bones are arranged in a flexible column in the _dorsal_ (the back) side of the body. This _vertebral column_, as it is called, is distinctive of all _vertebrates_. Within its bony protection lies the delicate central nervous system, and to this column are attached the big bones of the legs and arms. The vertebrate animals deserve more of our attention than other forms of life because man himself is a vertebrate.

Five groups or classes of vertebrates exist. _Fishes_, _Amphibians_, _Reptiles_, _Birds_, and _Mammals_. Let us see how to distinguish one class from another.

Fishes.--Fishes are familiar animals to most of us. We know that they live in the water, have a backbone, and that they have fins. They breathe by means of gills, delicate organs fitted for taking oxygen out of the water. The heart has two chambers, an auricle and a ventricle. They have a skin in which are glands secreting mucus, a slimy substance which helps them go through the water easily. They usually lay very many eggs.

CLASSIFICATION OF FISHES

ORDER I. _The Elasmobranchs._ Fishes which have a soft skeleton made of cartilage and exposed gill slits. Examples: sharks, skates, and rays.

ORDER II. _The Ganoids._ Fishes which once were very numerous on the earth, but which are now almost extinct. They are protected by platelike scales. Examples: gars, sturgeon, and bowfin.

ORDER III. _The Teleosts, or Bony Fishes._ They compose 95 per cent of all living fishes. In this group the skeleton is bony, the gills are protected by an operculum, and the eggs are numerous. Most of our common food fishes belong to this class.

ORDER IV. _The Dipnoi, or Lung Fishes._ This is a very small group. In many respects they are more like amphibians than fishes, the swim bladder being used as a lung. They live in tropical Africa, South America, and Australia, inhabiting the rivers and lakes there.

Characteristics of Amphibia.--The frog belongs to the class of vertebrates known as Amphibia. As the name indicates (_amphi_, both, and _bia_, life), members of this group live both in water and on land. In the earlier stages of their development they take oxygen into the blood by means of gills. When adult, however, they breathe by means of lungs. At all times, but especially during the winter, the skin serves as a breathing organ. The skin is soft and unprotected by bony plates or scales. The heart has three chambers, two auricles and one ventricle. Most amphibians undergo a complete metamorphosis, or change of form, the young being unlike the adults.

CLASSIFICATION OF AMPHIBIA

ORDER I. _Urodela._ Amphibia having usually poorly developed appendages. Tail persistent through life. Examples: mud puppy, newt, salamander.

ORDER II. _Anura._ Tailless Amphibia, which undergo a metamorphosis, breathing by gills in larval state, by lungs in adult state. Examples: toad and frog.

Characteristics of Reptilia.--These animals are characterized by having scales developed from the skin. In the turtle they have become bony and are connected with the internal skeleton. Reptiles always breathe by means of lungs, differing in this respect from the amphibians. They show their distant relationship to birds in that their large eggs are incased in a leathery, limy shell.

CLASSIFICATION OF REPTILES

ORDER I. _Chelonia_ (turtles and tortoises). Flattened reptiles with body inclosed in bony case. No teeth or sternum (breastbone). Examples: snapping turtle, box tortoise.

ORDER II. _Lacertilia_ (lizards). Body covered with scales, usually having two-paired appendages. Breathe by lungs. Examples: fence lizard, horned toad.

ORDER III. _Ophidia_ (snakes). Body elongated, covered with scales. No limbs present. Examples: garter snake, rattlesnake.

ORDER IV. _Crocodilia._ Fresh-water reptiles with elongated body and bony scales on skin. Two-paired limbs. Examples: alligator, crocodile.

Birds.--Birds among all other animals are known by their covering of feathers and the presence of wings. The feathers are developed from the skin. These aid in flight, and protect the body from the cold.

The form of the bill in particular shows adaptation to a wonderful degree. A duck has a flat bill for pushing through the mud and straining out the food; a bird of prey has a curved or hooked beak for tearing; the woodpecker has a sharp, straight bill for piercing the bark of trees in search of the insect larvae which are hidden underneath. Birds do not have teeth.

The rate of respiration, of heartbeat, and the body temperature are all higher in the bird than in man. Man breathes from twelve to fourteen times per minute. Birds breathe from twenty to sixty times a minute. Because of the increased activity of a bird, there comes a necessity for a greater and more rapid supply of oxygen, an increased blood supply to carry the material to be used up in the release of energy, and a means of rapid excretion of the wastes resulting from the process of oxidation. Birds are large eaters, and the digestive tract is fitted to digest the food quickly, by having a large crop in which food may be stored in a much softened condition. As soon as the food is part of the blood, it may be sent rapidly to the places where it is needed, by means of the large four-chambered heart and large blood vessels.

The high temperature of the bird is a direct result of this rapid oxidation; furthermore, the feathers and the oily skin form an insulation which does not readily permit of the escape of heat. This insulating cover is of much use to the bird in its flights at high altitudes, where the temperature is often very low. Birds lay eggs and usually care for their young.

CLASSIFICATION OF BIRDS

ORDER I. _Cursores._ Running birds with no keeled breastbone. Examples: ostrich, cassowary.

ORDER II. _Passeres._ Perching birds; three toes in front, one behind. Over one half of all species of birds are included in this order. Examples: sparrow, thrush, swallow.

ORDER III. _Gallinae._ Strong legs; feet adapted to scratching. Beak stout. Examples: jungle fowl, grouse, quail, domestic fowl.

ORDER IV. _Raptores._ Birds of prey. Hooked beak. Strong claws. Examples: eagle, hawk, owl.

ORDER V. _Grallatores._ Waders. Long neck, beak, and legs. Examples: snipe, crane, heron.

ORDER VI. _Natatores._ Divers and swimmers. Legs short, toes webbed. Examples: gull, duck, albatross.

ORDER VII. _Columbinae._ Like Gallinae, but with weaker legs. Examples: dove, pigeon.

ORDER VIII. _Pici._ Woodpeckers. Two toes point forward, two backward, and adaptation for climbing. Long, strong bill.

ORDER IX. _Psittaci._ Parrots, hooked beak and fleshy tongue.

ORDER X. _Coccyges._ Climbing birds, with powerful beak. Examples: kingfisher, toucan, and cuckoo.

ORDER XI. _Macrochires._ Birds having long-pointed wings, without scales on metatarsus. Examples: swift, humming bird, and goatsucker.

Mammals.--Dogs and cats, sheep and pigs, horses and cows, all of our domestic animals (and man himself) have characters of structure which cause them to be classed as mammals. They, like some other vertebrates, have lungs and warm blood. They also have a hairy covering and bear young developed to a form similar to their own,[28] and nurse them with milk secreted by glands known as the _mammary glands_; hence the term "mammal."

Footnote 28: With the exception of the monotremes.

Adaptations in Mammalia.--Of the thirty-five hundred species, most inhabit continents; a few species are found on different islands, and some, as the whale, inhabit the ocean. They vary in size from the whale and the elephant to tiny shrew mice and moles. Adaptations to different habitat and methods of life abound; the seal and whale have the limbs modified into flippers, the sloth and squirrel have limbs peculiarly adapted to climbing, while the bats have the fore limbs modeled for flight.

Lowest Mammals.--The lowest are the monotremes, animals which lay eggs like the birds, although they are provided with hairy covering like other mammals. Such are the Australian spiny anteater and the duck mole.

All other mammals bring forth their young developed to a form similar to their own. The kangaroo and opossum, however, are provided with a pouch on the under side of the body in which the very immature, blind, and helpless young are nourished until they are able to care for themselves. These pouched animals are called _marsupials_.

The other mammals may be briefly classified as follows:--

CLASSIFICATION OF HIGHER MAMMALS

ORDER I. _Edentata._ Toothless or with very simple teeth. Examples: anteater, sloth, armadillo.

ORDER II. _Rodentia._ Incisor teeth chisel-shaped, usually two above and two below. Examples: beaver, rat, porcupine, rabbit, squirrel.

ORDER III. _Cetacea._ Adapted to marine life. Examples: whale, porpoise.

ORDER IV. _Ungulata._ Hoofs, teeth adapted for grinding. Examples: (_a_) odd-toed, horse, rhinoceros, tapir; (_b_) even-toed, ox, pig, sheep, deer.

ORDER V. _Carnivora._ Long canine teeth, sharp and long claws. Examples: dog, cat, lion, bear, seal, and sea lion.

ORDER VI. _Insectivora._ Example: mole.

ORDER VII. _Cheiroptera._ Fore limbs adapted to flight, teeth pointed. Example: bat.

ORDER VIII. _Primates._ Erect or nearly so, fore appendage provided with hand. Examples: monkey, ape, man.

Increasing Complexity of Structure and of Habits in Plants and Animals.--In our study of biology so far we have attempted to get some notion of the various factors which act upon living things. We have seen how plants and animals interact upon each other. We have learned something about the various physiological processes of plants and animals, and have found them to be in many respects identical. We have found grades of complexity in plants from the one-celled plant, bacterium or pleurococcus, to the complicated flowering plants of considerable size and with many organs. So in animal life, from the Protozoa upward, there is constant change, and the change is toward greater complexity of structure and functions. An insect is a higher type of life than a protozoan, because its structure is more complex and it can perform its work with more ease and accuracy. A fish is a higher type of animal than the insect for these same reasons, and also for another. The fish has an internal skeleton which forms a pointed column of bones on the _dorsal_ side (the back) of the animal. It is a vertebrate animal.

The Doctrine of Evolution.--We have now learned that animal forms may be arranged so as to begin with very simple one-celled forms and culminate with a group which contains man himself. This arrangement is called the _evolutionary series_. Evolution means change, and these groups are believed by scientists to represent stages in complexity of development of life on the earth. Geology teaches that millions of years ago, life upon the earth was very simple, and that gradually more and more complex forms of life appeared, as the rocks formed latest in time show the most highly developed forms of animal life. The great English scientist, Charles Darwin, from this and other evidence, explained the theory of evolution. This is the belief that simple forms of life on the earth slowly and gradually gave rise to those more complex and that thus ultimately the most complex forms came into existence.

The Number of Animal Species.--Over 500,000 species of animals are known to exist to-day, as the following table shows.

Protozoa 8,000 Arachnids 16,000 Sponges 2,500 Crustaceans 16,000 Coelenterates 4,500 Mollusks 61,000 Echinoderms 4,000 Fishes 13,000 Flat-worms 5,000 Amphibians 1,400 Roundworms 1,500 Reptiles 3,500 Annelids 4,000 Birds 13,000 Insects 360,000 Mammals 3,500 Myriapods 2,000 ------- Total 518,900

Man's Place in Nature.--Although we know that man is separated mentally by a wide gap from all other animals, in our study of physiology we must ask where we are to place man. If we attempt to classify man, we see at once he must be placed with the vertebrate animals because of his possession of a vertebral column. Evidently, too, he is a mammal, because the young are nourished by milk secreted by the mother and because his body has at least a partial covering of hair. Anatomically we find that we must place man with the apelike mammals, because of these numerous points of structural likeness. The group of mammals which includes the monkeys, apes, and man we call the _primates_.

Although anatomically there is a greater difference between the lowest type of monkey and the highest type of ape than there is between the highest type of ape and the lowest savage, yet there is an immense mental gap between monkey and man.

Instincts.--Mammals are considered the highest of vertebrate animals, not only because of their complicated structure, but because their instincts are so well developed. Monkeys certainly seem to have many of the mental attributes of man.

Professor Thorndike of Columbia University sums up their habits of learning as follows:--

"In their method of learning, although monkeys do not reach the human stage of a rich life of ideas, yet they carry the animal method of learning, by the selection of impulses and association of them with different sense-impressions, to a point beyond that reached by any other of the lower animals. In this, too, they resemble man; for he differs from the lower animals not only in the possession of a new sort of intelligence, but also in the tremendous extension of that sort which he has in common with them. A fish learns slowly a few simple habits. Man learns quickly an infinitude of habits that may be highly complex. Dogs and cats learn more than the fish, while monkeys learn more than they. In the number of things he learns, the complex habits he can form, the variety of lines along which he can learn them, and in their permanence when once formed, the monkey justifies his inclusion with man in a separate mental genus."

Evolution of Man.--Undoubtedly there once lived upon the earth races of men who were much lower in their mental organization than the present inhabitants. If we follow the early history of man upon the earth, we find that at first he must have been little better than one of the lower animals. He was a nomad, wandering from place to place, feeding upon whatever living things he could kill with his hands. Gradually he must have learned to use weapons, and thus kill his prey, first using rough stone implements for this purpose. As man became more civilized, implements of bronze and of iron were used. About this time the subjugation and domestication of animals began to take place. Man then began to cultivate the fields, and to have a fixed place of abode other than a cave. The beginnings of civilization were long ago, but even to-day the earth is not entirely civilized.

The Races of Man.--At the present time there exist upon the earth five races or varieties of man, each very different from the other in instincts, social customs, and, to an extent, in structure. These are the Ethiopian or negro type, originating in Africa; the Malay or brown race, from the islands of the Pacific; the American Indian; the Mongolian or yellow race, including the natives of China, Japan, and the Eskimos; and finally, the highest type of all, the Caucasians, represented by the civilized white inhabitants of Europe and America.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_, American Book Company. Bulletin of U. S. Department of Agriculture, _Division of Biological Survey_, Nos. 1, 6, 13, 17. Davison, _Practical Zoology_. American Book Company. Ditmars, _The Reptiles of New York_. Guide Leaflet 20. Amer. Mus. of Nat. History. Sharpe, _A Laboratory Manual in Biology_, pp. 140-150, American Book Company. Walker, _Our Birds and Their Nestlings_. American Book Company. Walter, H. E. and H. A., _Wild Birds in City Parks_. Published by authors.

ADVANCED

Apgar, _Birds of the United States_. American Book Company. Beebe, _The Bird_. Henry Holt and Company. Ditmars, _The Reptile Book_. Doubleday, Page and Company. Hegner, _Zoology_. The Macmillan Company. Hornaday, _American Natural History_. Jordan and Evermann, _Food and Game Fishes_. Doubleday, Page and Company. Parker and Haswell, _Textbook of Zoology_. The Macmillan Company. _Riverside Natural History._ Houghton, Mifflin and Company. Weed and Dearborn, _Relation of Birds to Man_. Lippincott.

XV. THE ECONOMIC IMPORTANCE OF ANIMALS

_Problems.--I. To determine the uses of animals._ _(a) Indirectly as food._ _(b) Directly as food._ _(c) As domesticated animals._ _(d) For clothing._ _(e) Other direct economic uses._ _(f) Destruction of harmful plants and animals._ _--II. To determine the harm done by animals._ _(a) Animals destructive to those used for food._ _(b) Animals harmful to crops and gardens._ _(c) Animals harmful to fruit and forest trees._ _(d) Animals destructive to stored food or clothing._ _(e) Animals indirectly or directly responsible for disease._

LABORATORY SUGGESTIONS

Inasmuch as this work is planned for the winter months the laboratory side must be largely museum and reference work. It is to be expected that the teacher will wish to refer to much of this work at the time work is done on a given group. But it is pedagogically desirable that the work as planned should be _varied_. Interest is thus held. Outlines prepared by the teacher to be filled in by the student are desirable because they lead the pupil to individual selection of what seems to _him_ as important material. Opportunity should be given for laboratory exercises based on original sources. The pupils should be made to use reports of the U. S. Department of Agriculture, the Biological Survey, various States Reports, and others.