SAINT VALENTINE'S DAY

DEFINITION: Feb. 14, observed in honour of a martyr of the 3d cent. and, coincidentally, as a day for sending valentines to sweethearts, schoolmates.

People once believed that birds, particularly love-birds, began to mate on February 14. In ancient Rome the festival of the Lupercalia was celebrated on February 15; the festival involved fertility rites and honoured the two Roman gods Juno and Pan. In modern times it is customary to exchange cards and other gifts with loved ones, close friends, and family members on February 14. The day is called St. Valentine's Day. The holiday apparently has no connection with the two martyred St. Valentines of 3rd-century Rome except that their feast days also are celebrated on February 14.

Lupercalia, Roman festival in honour of ancient god Lupercus, protector of flocks against wolves, sometimes identified with Faunus.

The modern celebration of St. Valentine's Day probably grew out of a tradition that started in about the 14th century. For many years young people in France and England would get together on St. Valentine's Eve. Each person became the "valentine" of the one whose name was drawn from a valentine box.

OAKS

DEFINITION: 1 any of a genus (Quercus) of large hardwood trees and bushes of the beech family, bearing acorns 2 the wood of an oak 3 any of various plants with oak like leaves 4 a wreath of oak leaves 5 woodwork, furniture, etc. made of oak.

The majestic monarchs of the forest may take 100 years to reach maturity and then may live for another 900 years. Their wood provides one of the strongest and most durable of timbers.

Oaks range in size from shrubs to giants 150 feet (45 meters) high. The trees develop thick trunks and large, wide-spreading branches. The leaf is usually deeply lobed, but in some species it is almost smooth at the edge. Oaks are easily recognized by their fruit the acorn, a round nut set in a woody cup. American Indians and New England pioneers boiled and ate the acorns of the white oak, and acorns are part of the diet of some forest and tree-dwelling animals.

About 450 species of ornamental and timber oaks constitute the oak genus Quercus (a member of the beech family Fagaceae). They grow widely throughout the Temperate Zone of the Northern Hemisphere and at high altitudes in the tropics. About 75 species are native to the United States.

White oak, name (Quercus alba) applied to the group of oaks with grey-brown heartwood, usually without a reddish tinge, and with pores filled with a fibrous growth that makes this wood resistant to decay; includes the species white, swamp white, chestnut, swamp chestnut, chinquapin, bur, live, and post oaks.

One of the best-known species in the United States is the white oak (Q. alba). This stately tree grows from 70 to 150 feet (21 to 45 meters) high. The leaves are large and deeply lobed, light green above and whitish beneath. In autumn the foliage turns deep violet and clings to the tree throughout the winter, falling only just before new leaves appear. This is characteristic of many oaks. The trunk of the white oak, which often is 4 feet (1.3 meters) in diameter, has furrowed whitish bark; this gives the tree its name.

The bur, or mossy-cup, oak (Q. macrocarpa) is the most common oak of the prairie states. Its average height is about 75 feet (23 meters), but some bur oaks tower to 150 feet (45 meters). Its deep-green leaves are very large, sometimes up to 1 foot (0.3 meter) in length, deeply lobed at the lower part and rounded at the apex.

The acorns are large and set in rough fringed cups. The bur oak grows from Pennsylvania to Montana and is largest in the Ohio Valley.

Red oak, name Quercus rubra or Quercus borealis applied to the group of oaks with brown wood that has a red tint; includes the species northern red, southern red, swamp red, scarlet, black, blackjack, laurel, pin, shumard, water, and willow oaks.

The red oak (Q. rubra, or Q. borealis) is colourful in all seasons. The round solid crown of the tree is covered with large, sharply lobed leaves. These are pink and furry in the spring, green in the summer, and deep purple-red in the autumn. The bark is dark brown, thick, and furrowed. The red oak bears large acorns set in shallow saucer like cups.

The pin oak or Spanish oak (Q. palustris) is a quick-growing medium sized tree raised generally as a street tree. Its deeply cut leaves are brilliant in autumn. The trunk and larger limbs are studded with tough branchlets, which probably account for the tree's name. It grows in the Eastern United States, usually on moist lowlands.

Chestnut, Live, and English Oaks

The chestnut oak (Q. muehlenbergii or Q. acuminata), also called the yellow oak, has the major characteristics of the oak family but has chestnut like leaves. These are serrated, or saw-toothed, instead of deeply lobed. The tree is tall and stately, with stout trunk and limbs. It grows in the central states.

The live oak (Q. virginiana) is a beautiful southern tree that sometimes reaches 60 feet (18 meters) in height. Its branches are spreading and graceful, covered with small evergreen foliage and often festooned with mosses. It rarely grows far from the Gulf of Mexico.

The well-known English oak (Q. robur) is the largest and most celebrated of all the world's oak trees. The "wooden walls" of Britain, the ships of the Royal Navy, were built from the timber of this kingly tree. Some fine specimens still standing in England date from the Anglo-Saxon period. The majestic English oak is a veritable giant, with sturdy limbs and enormous girth. The peculiar zigzag growth of the limbs in older trees gives them a twisted look and adds to their picturesque appearance.

Uses

Tannin (or tannic acid), organic chemical compound used in tanning leather, dyeing fabric, making ink, and in various medical applications.

The value of oak timber varies with the species. The English oak is tough, hard, close grained, and comparatively easy to work. It is exceedingly durable and defies drought and moisture. The bur oak ranks next to the English oak in importance. It is used for shipbuilding, furniture, and other manufactures. The bark is especially rich in tannin and is used in the preparation of leather. The timber of the white oak is adapted to the same purposes as that of the English oak and the bur oak, though it is slightly inferior in quality.

The live oak produces strong yellow wood that is difficult to work. It is highly valued for shipbuilding, however, because it is very durable under water. The timber of the red oak is porous and so has little commercial value, but it is useful for making barrels, and the bark is used for tanning leather. The chestnut oak also yields good timber.

Galls

Gall (or gall nut), abnormal growth on leaves, stems, buds, flowers, or roots of plants caused by various parasites, especially insects and mites, and more rarely by nematodes, bacteria, fungi, slime moulds, and algae; found on almost all forms of plant life, but especially common on oak trees, willows, roses, and goldenrod.

The galls or gall nuts so frequently found on oaks are usually produced by gall flies They lay their eggs in the tissues of the trees. The tissues swell at the point of puncture and form firm nut like structures within which the young of the insects develop to maturity. Each kind of gall fly produces a different kind of gall. Some galls are rich in tannin.

FLIES

DEFINITION: 1 a) any dipterous insect; esp., the housefly b) any of several four-winged insects from various orders, as the mayfly or caddis fly 2 a hook covered with feathers, coloured silk, etc. to resemble an insect, used as a lure in fishing: a wet fly drifts below the surface of the water, and a dry fly floats on it 3 Printing a device on a flat bed press for removing and stacking the printed sheets.

While some flies are beneficial to humans as parasites of insect pests or as scavengers and many others are important as plant pollinators, flies are also known to be carriers of such serious diseases as cholera, typhoid, and dysentery. In most species of fly the body and padded feet are covered with bristling hairs and the tongue is coated with sticky glue.

Under a powerful microscope, samples of the dust and dirt clinging to these hairs reveal bacteria that cause a wide variety of diseases. Flies get the germs from garbage and sewage. If they touch food later, it too may become contaminated.

Flies can multiply at an incredibly fast rate. Between the months of April and August one female fly could have more than 190 quintillion descendants if all her female offspring and their descendants lived. Although this does not happen, plenty of flies will be produced every summer if only one female in a hundred escapes death long enough to lay eggs. The only effective way to keep down the number of flies is to prevent breeding.

Long exposure to freezing weather kills flies. In cold climates only a few fertile females hibernating in sheltered places survive the winter. Warm weather awakens them and they seek moist spots such as manure piles or garbage in which to lay their eggs.

Maggot, larva of an insect; term most often applied to larva that lives in decaying matter.

The eggs look like tiny white grains of wheat, about 1/20 of an inch (0.13 centimetre) long. The female lays up to 250 eggs in several clusters. Within 24 hours the eggs hatch into white larvae, or maggots. These feed and grow for about five days, then become pupae. Some five days later an adult fly emerges from the pupa case. In two or three days each new female is ready to lay eggs. The entire life cycle takes about two weeks to complete.

The Right Way to Get Rid of Flies

Once flies are established in a locality, they can be suppressed only by eliminating the places in which their eggs can hatch and the maggots can feed. If manure and garbage are removed from a location and destroyed regularly and if garbage cans are kept covered the population of houseflies in that location can be kept to a minimum. If this regular removal schedule is not possible, garbage can be kept in fly-proof containers of sheet metal or screening while awaiting collection. Manure piles can also be treated with suitable chemicals for example, calcium cyanamide and calcium super phosphate (acid phosphate) to keep them from attracting flies.

People can protect themselves from any surviving flies by putting screens on their doors and windows, by swatting, or by applying any of various chemical sprays or dusts, particularly those containing pyrethrum. Insecticides should be used with care to avoid contamination of food, dishes, and utensils.

The Physical Characteristics of Flies

The adult fly is about one-quarter inch (0.64 centimetre) long and about half an inch (1.27 centimetres) across the outspread wings. A thousand adults weigh less than an ounce.

Each foot on its three pairs of legs is equipped with claws and two hairy pads called pulvilli. These pads secrete a sticky liquid that enables the fly to cling to almost any surface and run upside down along a ceiling.

A fly has five eyes. Two of these are huge compound structures that cover most of the head. Between these are three tiny simple eyes, set in a triangle. A flys vision, however, is not sharp. It relies more upon its acute sense of smell to locate its food.

The mouth parts are adapted for sucking up liquid food. A long "tongue" has two pads, or lobes, at the end, which act as funnels for drawing in liquid. The fly can also turn soluble foods such as sugar into liquids by spreading saliva on them. Unlike the bloodsucking sand flies, or stable flies (Stomoxys calcitrans), which they resemble, houseflies have no equipment for biting.

Some Relatives of the Housefly

Most two-winged insects (Diptera) are properly called flies. In place of the second pair of wings possessed by bees, dragonflies, and many other insects, true flies have club-shaped balancers (halteres). About 45,000 members of the order Diptera are known; some 11,000 are found in North America.

Stable fly, bloodsucking fly inhabiting stables; often enters houses.

Next to the housefly (Musca domestica), the most widespread and annoying members of the order are probably the mosquitoes. Some of these rank also among the deadly disease carriers. Sand flies, usually found in wet regions, transmit disease by biting. Another dangerous biter is the tsetse fly of central Africa.

Mediterranean fruit fly (or medfly), destructive insect (Ceratitis capitata); attacks fruit, nuts, and vegetables; yellow, black, and white markings; lays as many as 500 eggs in citrus fruits (except lemons and sour limes); larvae tunnel into the flesh of the fruit making it unfit for human consumption; discovered in Florida in 1929; thought to have been eradicated in the United States by 1930; reappeared in 1956 and in the early 1960s and again, in California, in 1981; worldwide quarantine laws were formed because of this pest to regulate the entry of fruits into countries; heavy U.S. infestation in 1981 set off heated controversy between fruit growers and environmentalists; the aerial-spraying program that was finally adopted sparked renewed debates worldwide about the eradication of costly insect pests.

Much damage is done by fruit flies in tropical and semitropical climates. Especially harmful is the Mediterranean fruit fly (Ceratitis capitata). The fruit fly called Drosophila melanogaster has proved extremely useful in studies of heredity. It passes through its life cycle in a few days. The results of selective breeding, of diet, and of other influences can be observed within a short time.

Midges, group of flies belonging to the order Diptera, family Chironomidae; mosquito like in form but more delicate.

Horsefly (also called gadfly), a two-winged fly of the order Diptera, family Tabanidae; usually about 3 times size of housefly; has pointed proboscis; only females suck blood; males sip plant sap or nectar.

Flesh flies breed and lay their eggs in stored meats; bot flies, or heel flies, torment cattle, sheep, and horses; gall gnats damage fruit. Other annoying or vicious flies are the tiny midges, including the "punkies," or "no-see-ums" (Ceratopogon guttipennis), of the northern woods; the swarming black flies (Simulium hirtipes), which have been known to drive animals into fatal frenzies; horseflies, which also bite humans; and the so-called bee lice, bat ticks, and sheep ticks, which are parasites and so have lost their wings.

More useful members of the order are the syrphus flies, which resemble bumblebees and wasps and destroy plant lice; drone flies, whose larvae live in foul water, eating decaying vegetable matter; and robber flies, which consume other insects. Less-known members of the group are the louse flies, the nimble flies, the humpbacked flies, the March flies, and the false crane flies.

Flies are among the oldest of insects. Their fossil remains are found in rocks of early geologic ages and may also be preserved in ancient amber.

BUBONIC PLAGUE

DEFINITION: a contagious disease, the most common form of plague, caused by a bacterium (Yersinia pestis ) transmitted by fleas from infected rats, and characterized by buboes, fever, prostration, and delirium.

Black Death a deadly disease, probably bubonic plague, which devastated Europe and Asia in the 14th cent.

1337: Hundred Years' War begins. Two basic issues created the antagonism between England and France in the middle of the 14th century: the succession to the French throne and the extent of British possessions in France. In 1336 the flame that lit the fire was French king Philip VI halt of the thriving wool trade between England and France.

The resulting war which would be known as the Hundred Years' War was not a continual struggle but an intermittent one that actually lasted more than a century. Charles V of France died in 1328 leaving no successor. There were two claimants to the throne: Edward III of England, who was also duke of Guyenne in France; and the count of Valois. A French assembly chose the count, who took the name Philip VI. This could have been the end of the matter, but the new king chose to confiscate Edward's territory of Guyenne. Edward then asserted his claim to the throne of France by sending an army to Flanders in 1337.

Notable among the events of the war were: the battles of Crecy in 1346 and Agincourt in 1415, both were unexpected victories for the English; the interruption of fighting due to the spread of the bubonic plague in 1348; and the involvement of Joan of Arc inspiring the French to victory at Orleans in 1429. Eventually France won the war, but at great cost to the land and its people.

England retained only the city of Calais, which it gave up in 1558.

This long war inspired much literature, including plays by William Shakespeare and George Bernard Shaw. Dramatic accounts of St. Joan have proved particularly appealing to audiences.

1347: Black Death. The plague is one of the most devastating diseases that has ever afflicted mankind. It is a highly contagious fever caused by the bacillus Yersinia pestis, which is carried by fleas that infest rats.

The plague, commonly called bubonic plague or the Black Death, has been known since ancient times, but the best documented instance was its deadly appearance in Europe in 1347. It raged throughout all of Europe, killing at least one-fourth of the population probably 25 million people. Without understanding how it is spread, people had no defence against the disease. Poor sanitary conditions and the disruption of war only worsened the epidemic.

In Europe the epidemic started in Sicily and was spread by shipboard rats to other Mediterranean ports. It moved to North Africa, Italy, Spain, England, and France. By 1349 it made its way to Austria, Germany, Switzerland, and the Low Countries. By 1350 it reached Scandinavia and the Baltic states.

In general, the population of Europe did not recover to its size before the plague until the 16th century, and some towns never recovered. The immediate results of the plague a general collapse of economies, a breakdown of class relationships, and a halt to wartime hostilities forced a massive restructuring of society. It has had a lasting impact on art, literature, and religious thought.

Caused by rod-shaped bacteria Yersinia pestis (Pasteurella pestis), bubonic plague is an acute and severe infection. Plague is initially spread by the bite of a flea from an infected rodent (rat, squirrel), and passed from person to person by mucus droplets spread from coughing. When infected by plague bacteria, a person becomes ill within a few hours to a few days. They spread through the body, causing high fever, swollen lymph nodes, rash, and changes in blood pressure. Other forms of plague are pneumonic, which causes severe pneumonia, and septicaemic All forms of plague are extremely dangerous.

The plague bacteria cause a massive infection that overwhelms the body's defences When plague is untreated, many victims die within a few days. Treatment is with antibiotics such as tetracycline and streptomycin and is begun immediately when infection from plague is suspected. People are immunized against plague before they travel into areas where plague is endemic (always present). Control of plague requires the control of wild rodents. Insect repellents are used against flea bites.

During the 1300s nearly half the population of Europe was killed by an epidemic of plague. The disease was called the Black Death, which described the dark colour of many victims' faces after death. Plague still occurs in most of the world, but epidemics such as those of earlier centuries are fortunately not seen. Public health departments of all countries do all they can to avert plague epidemics.

Recommended reading includes 'The Outline of History', by H.G. Wells, which was first published in 1920. Volume 2 of the revised edition (1971) of this famous work contains information related to this article. Also recommended is the current edition of 'The Merck Manual'.

Assisted by Ann Giudici Fettner

ICHNEUMON FLY

DEFINITION: any of a large family (Ichneumonidae) of hymenopteran insects whose larvae live as parasites in or on other insect larvae Also ichneumon wasp.

The graceful, four-winged ichneumon fly is not truly a fly. The insect is a relative of wasps, ants, and bees. The female lays her eggs on or near the eggs, larvae, and pupae of harmful insects. The ichneumon larvae that hatch from the eggs feed on the other larvae and pupae and kill them.

Ichneumon flies vary in size, but all have long, slender abdomens with long legs that trail gracefully as the insect flies through the air. From the abdomen of the female extends a threadlike egg-laying organ called an ovipositor (egg depositor).

These insects belong to the family Ichneumonidae of the order Hymenoptera. More than 3,300 species in the family Ichneumonidae have been described. Specimens from the genus Megarhyssa can measure 10 inches (25 centimetres) in length.

ANIMALS (Part 1 of 4)

Cheetah

DEFINITION: 1 any living organism, excluding plants and bacteria: most animals can move about independently and have specialized sense organs that enable them to react quickly to stimuli: animals do not have cell walls, nor do they make food by photosynthesis 2 any such organism other than a human being, esp. a mammal or, often, any four-footed creature 3 a brutish, debased, or inhuman person 4 [Colloq.] a person, thing, concept, etc. thought of as a kind or type [today's athlete is another animal altogether]

All living things are divided into two main kingdoms the animal and plant kingdoms and two or three other kingdoms that include bacteria, blue-green algae, and one-celled creatures with definite nuclei. What is the difference between a horse, for example, and grass? A horse moves about in the pasture eating grass. It trots toward you when you offer it a lump of sugar and shows pleasure when you stroke its head. The grass, however, is rooted to one place. It does not respond behaviourally to people or to the horse in any way.

Animals Move About and Sense Surroundings

Adult animals move freely from place to place during at least one phase of their life. Plants usually cannot move unless a force, such as the wind, causes them to move.

Most animals move freely from place to place and can sense their surroundings; that is, they can taste, smell, hear, see, and touch. Certain simple animals, such as the corals and barnacles, spend most of their lives fastened to one spot, but they are able to swim freely when they are young. Even these rooted animals have parts that move in order to capture food. Plants, however, cannot shift about at their own will. They react to heat, light, chemicals, and touch, but their responses are involuntary and automatic, quite different from those of animals.

All living things are made of cells. The walls of plant and animal cells are different.

Cellulose, complex carbohydrate consisting of 3,000 or more glucose units; basic structural component of plant cell walls; 90% of cotton and 50% of wood is cellulose; most abundant of all naturally occurring organic compounds; indigestible by humans; can be digested by herbivores, such as cows and horses, because they retain it long enough for digestion by micro organisms present in their digestive systems; also digestible by termites; processed to produce papers and fibres; chemically modified to yield plastics, photographic film, and rayon; other derivatives used as adhesives, explosives, thickening agents, and in moisture-proof coatings.

All living things are made up of cells of protoplasm. They may consist of a single cell, as does an amoeba, or billions of cells, as do trees and horses. The cell wall of a plant is composed of a woody material called cellulose. No true animal contains cellulose. Animal cells are bounded by a membrane composed chiefly of fat and protein.

Green plants make their own food. With the aid of the green substance called chlorophyll, they use the energy in sunlight to change carbon dioxide and water into carbohydrates and other food materials. No true animal contains chlorophyll.

Animals must eat, either directly or indirectly, the food manufactured by members of the plant kingdom. A horse cannot stand in the sun and wait for its body to make fat and proteins. It must move about the pasture in search of green grass. Even meat eaters for example, lions live on animals, such as zebras, which in turn subsist on plants.

The Variety of Animal Life

More than a million different kinds of animals inhabit the Earth. The exact number is not known, for new kinds are continually being discovered. They live in the seas, from the surface down to the black depths where no ray of light penetrates. On mountaintops and in deserts, in mud and in hot pools some form of animal life may be found.

Animals are infinitely varied in form, size, and habits. The smallest animals are bits of protoplasm that can be seen only with a microscope. The largest, the blue whales, may be more than 100 feet (30 meters) long and weigh 300,000 pounds (136,000 kilograms).

Some of the most familiar animals, such as dogs, birds, frogs, and fish, have a backbone and a central nervous system. They are called vertebrates, meaning animals with backbones. Animals without backbones are called invertebrates and include arthropods, worms, molluscs, and many other groups. Most of the vertebrates and many invertebrates have a head where sense organs are concentrated and have legs, wings, or fins for locomotion. Vertebrates and many invertebrates, such as the arthropods and worms, have bilateral, or two-sided, symmetry. This means that they have two mirror-image sides (a right side and a left side), distinct upper and lower surfaces of the body, and a distinct front and rear.

Some invertebrates, such as jellyfish, sea anemones, and starfish, display radial symmetry, in which the parts of the body are arranged around a central axis, similar to a wheel.

Animals with radial symmetry live in marine or freshwater aquatic environments. Some drift with the currents, unable to swim in any definite direction. Others become attached to a solid object by one end and float with the mouth end upright. Tentacles arranged in a circle around the mouth sweep in food particles and ward off enemies.

One-celled animals called protozoans live in fresh and salt water. Many are shapeless creatures and cannot swim toward their food. They move along by squeezing out a finger like projection from the body. This is called a pseudopod, from the Greek meaning "false foot." The pseudopod fastens to something solid, and the rest of the body flows into the fastened projection. The amoeba also moves in this manner. One-celled animals are very small. They are single blobs of liquid enclosed in a thin membrane and as such cannot attain a large size or a very definite shape.

Animals with Outside Skeletons and Feet

Molluscs have soft bodies that are not divided into specialized sections such as head, thorax, and abdomen. Many molluscs are enclosed in hard, hinged shells. Snails have a single large, fleshy foot located on the stomach side.

The heads of the octopus and the squid are surrounded by a circle of eight or ten tentacles that act as arms and feet. Oysters, clams, mussels, and scallops all have a single axe-shaped foot which they burrow into sand.

Most molluscs do not move around efficiently. Oysters fasten themselves to something solid and settle down for life, letting food drift to them. Scallops may move in zigzag leaps by clapping their shells together.

Joint-Legged Animals

Arthropod, animal of the phylum Arthropoda comprising invertebrates with external skeleton, segmented body, and jointed appendages.

Joint-legged animals, or arthropods, have bodies divided into segments that have specialized functions. These animals also have many jointed legs. Most arthropods are covered with a jointed skeleton made of a horny material. This outside skeleton is lighter than the shells of the molluscs The legs and muscles and many organs of the arthropod are attached to the outside skeleton.

The arthropods include insects, lobsters, crabs, centipedes, millipedes, scorpions, and spiders. They can run, jump, swim, and crawl. Some live mostly on land, while others live mostly in water. Many of the insects have wings and can fly. Arthropods inhabit most of the Earth's environments, from the poles to the tropics, and are found in fresh and marine water and in terrestrial habitats.

How Back boned Animals Move

Vertebrates move through water and air and over the ground with great speed and skill. Birds, with their feathered wings, are the best fliers. Fish are the best swimmers. However, other vertebrates also can fly and swim. Bats fly on wings of membrane like skin. The flying squirrel glides on a broad membrane between its legs. The flying fish soars over the surface of the ocean by using its fins. Neither the fish nor the squirrel can soar great distances, however.

Some turtles swim with paddle like front legs. Some water birds can swim underwater with their wings. The mud skipper and walking catfish are fishes that walk on mud by pulling themselves along on their front fins.

Frogs, kangaroos, various cats, and some fishes are superior jumpers. Salmon leap up waterfalls when they travel from the sea to their home streams to lay their eggs. Tarpon, swordfish, and sailfish make great leaps out of the water when pursuing their prey or trying to escape an enemy.

Breathing

Animals breathe in different ways:

• Some animals, like amoeba and sponges, let oxygen move through their cell walls.
• Fish and tadpoles breathe with their gills.
• Insects bring air in through pores, or holes, called spiracles.
• Mammals, birds, and reptiles breathe with lungs.

All animals must take in oxygen in order to change food into a form that the body can use. One-celled animals that live in water absorb oxygen directly through their membranes. The sponge is a very simple many-celled animal. The surface of a sponge is covered with millions of tiny pores. Water bearing dissolved oxygen and minute food particles flows through the pores and out of the opening at the top of the sponge.

Fish and tadpoles breathe by means of gills. Insects and caterpillars take air into the body through breathing pores called spiracles.

Mammals, birds, and reptiles obtain oxygen from the air. They take it into the lungs, and the oxygen passes through membranes in the lungs into particles called red blood cells. The bloodstream then carries the oxygen to all parts of the body. Amphibians have lungs, but they also have thin, moist skins that absorb oxygen directly.

Reproduction

Sea squirt, a tunicate or saclike marine animal, so called from its habit of ejecting water when touched; belongs to the phylum Chordata.

Hydra, primitive water animal of the class Hydrozoa and the genus Hydra.

All animals reproduce their own kind. One of the most primitive forms of reproduction is by fission, in which the individual organism divides to produce a replica of itself. Some animals, such as sea squirts, reproduce by budding: lumps appear along a branchlike organ and develop into young sea squirts. Sea squirts, sponges, corals, and other creatures that bud often remain together and form large colonies. The hydra also reproduces by budding, but in time the young bud separates and goes off to live alone.

Most animals reproduce by means of eggs from the female that are fertilized by sperm from the male. The eggs of some species are deposited in a nest or in some other manner before hatching. Most species of mammal and some species of reptile and fish bear their young alive, the fertilized eggs being retained within the body of the female.

The types of reproductive behaviour among animals are almost as varied as the kinds of animals themselves. Some species, such as most insects and turtles, deposit their eggs and give them no further attention. In colonies of the social insects, such as ants and bees, a single female lays all of the eggs, and workers provide care and nourishment for the developing young in the nest. The females of some reptiles, such as the king cobra and the blue-tailed skink, and amphibians, such as the marble salamander, stay with their clutch of eggs until they hatch but provide no protection or nourishment for the young. Some fish guard their young after they are born. Crocodilians protect the eggs before hatching and the young for several months afterwards. Many birds provide not only protection but also nourishment for the developing young. Mammals, which feed their young with milk produced by the mother, provide care for their young much longer than do other classes of animals.

ANIMALS (Part 2 of 4)

Homes

Many animals build temporary or permanent homes for themselves and their young. Birds occupy their nests only while they are incubating eggs and feeding the helpless nestling’s A few fish make temporary nests for their young.

No animal dwelling has excited more wonder and interest than the lodge built by the beaver. Almost as remarkable is the dome-shaped winter home of the muskrat.

Underground burrows with sleeping rooms, food-storage rooms, connecting tunnels, and emergency exits are constructed by ground hogs, prairie dogs, European rabbits, gophers, kangaroo rats, and field mice. Chimpanzees and gorillas build temporary nests and sleeping platforms of sticks in trees. The living quarters made by the different kinds of ants can be intricate and complex. Certain tropical bats cut palm fronds in such a way that they droop to form a leafy shelter from the hot sun and torrential rains.

Defences

All animals have some means of defending themselves against enemies. A cat can usually outrun a dog and climb the nearest tree. If cornered, it will scratch and bite.

Moose, largest member of the deer family; called elk in Europe.

Many animals rely on speed, camouflage, teeth, claws, and even intimidation to escape other animals. The variety of means of protection is extensive. Porcupines and hedgehogs roll into a ball and raise their sharp quills. The quills come off and stick into the nose or paw of an unwary dog or some other enemy. Skunks spray a foul-smelling fluid from a gland when they are frightened. Deer, moose, and antelope fight with their antlers. An elephant's trunk is a powerful weapon. It can be used to pick up another animal and smash it to the ground.

Squids shoot out a cloud of inky material and escape under its cover. Torpedo fish and several other kinds of fish have built-in electric storage cells by which they can deliver a paralysing shock. Some insects, snakes, and lizards protect themselves with their venom.

Many amphibians produce poisonous skin secretions.

Many animals hide by means of protective colouration A baby deer is almost invisible in the forest because its spotted coat looks like patches of sunlight in the brown leaves. Many fishes, birds, insects, lizards, and snakes use nature's camouflage to avoid being seen.

Feeding Behaviour

Vorticella (popularly called bell animalcules), genus of bell-shaped Protozoa.

Heliozoan, any protozoan of the order Heliozoa; often called sun animalcule; a single pseudopod may engulf food or several may work together.

Cilia (plural of cilium), hairlike, vibratory appendages found in some plants and animals.

Many one-celled animals (the vorticella and collar flagellate, for example) live in water. These very tiny animals and their feeding habits can be studied only under a microscope.

They feed on even tinier organisms in the water. The vorticella is attached by its stalk to some solid object. At the upper end is a mouth surrounded by tiny hairs called cilia. The hairs sweep food particles into the mouth by setting up a whirlpool action in the water. The food is enclosed in a bubble called a food vacuole, where it is digested.

Flagellum (plural flagella), a whip like extension of certain protozoans.

The collar flagellate has a delicate, transparent collar. From the centre of it grows a whip like organ, the flagellum. The beating of the whip draws a current of water toward the cell. Food particles in the current pass through the wall of the cell into the food vacuoles.

The heliozoan, also called sun animal, moves about and captures food by means of pseudopodia. In this case the pseudopodia are stiff spines that radiate from the centre of the cell. The spines wrap around the food and enclose it in a vacuole.

Hydra, primitive water animal of the class Hydrozoa and the genus Hydra.

The hydra feeds most commonly on the larva of a kind of shellfish. It has a mouth surrounded with long tentacles. The tentacles sting and paralyse the prey and then shove it inside the mouth.

Common swallow (in North America, barn swallow), bird (Hirundo rustica).

Butterflies and moths have tube like mouth parts. With these they suck nectar from flowers. Grasshoppers and beetles have chewing, grasping, and tearing mouth parts

Birds and bats catch insects in flight. Woodpeckers hammer into the bark of trees for grubs, other birds comb the leaves with their bills for small insects, and hawks swoop down on rodents and on other birds.

The kangaroo rat is a harmless little animal that lives in the deserts of the south western United States. It lives on dry thistle and cactus leaves, seeds, and small juicy tubers that grow abundantly in the desert 1 to 2 inches (2.5 to 5 centimetres) below the surface. It collects seeds in its cheek pouches and stores them in underground chambers. Gophers and chipmunks also collect food in their cheek pouches and store it in underground pantries for future use.

Carnivores, Herbivores, Insectivores

Animals that eat other animals are called carnivores. The shark is a fierce carnivore. It lives on smaller fish, such as mackerel. Many mammals are carnivores. They all have special kinds of teeth for tearing their food into chunks and chewing it. Most of them have claws for catching and holding their prey. Among the carnivores are cats, dogs, raccoons, weasels, bears, hyenas, and civet cats. Some fish subsist on plant and animal life known as plankton. The baleen whale is an enormous animal, growing up to 100 feet long. It feeds upon shrimp like creatures only about 1 inch in length. When it finds a school of shrimp, it opens its mouth and gulps in several barrels of water. Horny strainers that hang from the roof of its mouth catch the shrimp and drain out the water.

A large group of animals are plant eaters (herbivores). Many herbivores are prey of the carnivores. Insects are the dominant herbivores in most parts of the world, although they may be less conspicuous than plant-eating mammals and birds. Herbivorous mammals include horses, cattle, sheep, goats, rabbits, rodents, elephants, deer and antelope, and monkeys and apes.

A few mammals live on insects moles, shrews, and hedgehogs, bats, armadillos, aardvarks, and anteaters. Many bird species are insect eaters, as are certain kinds of insects, such as ladybugs.

How Animals Sense Their Surroundings

The ability of animals to sense and respond to their surroundings is one way in which they differ from plants. Higher animals have sense organs to perceive light, sound, touch, taste, and smell.

Eyes are very important to most mammals. Animals that hunt and feed by night have very large eyes. Cats' eyes have pupils that can open wide in the dark and narrow down to slits in the sunlight. Insects have compound eyes, made up of tiny units that break up the image into many small pictures. They also have two or three simple eyes that probably detect motion. The eyesight of some fish is especially keen.

Fennec fox, name of several species of small, fox like animals characterized by large pointed ears.

Ears are perhaps as important as eyes to some species. The fennec is a fox like animal that lives in the Sahara and hunts by night. Its large ears help it detect its prey in the darkness of a hot, dry climate, where food may be very scarce. The cat is also a night prowler, and it too has large, erect ears. The hearing organs of the field cricket and katydid are located on their forelegs. The organ is a thin membrane that vibrates in response to sound waves.

Many animals have sense organs unlike those of the mammals. The antennae of the moths, butterflies, and other insects seem to correspond to the organs of taste, touch, smell, and hearing.

Barbel, a soft, slender feeler around mouth of certain fishes, such as catfish, cod, drum fish, goat fish,

sturgeon.

The barbels of the catfish and the whiskers of the flying squirrel and the cat are organs of touch. They are very useful for animals that explore in the dark. The lateral line of the fish is a rod of nerve cells running the length of the body. It probably helps the fish feel movements in the surrounding water.

The delicate forked tongue of the snake tastes the air. With it the snake can locate food and other snakes. The rattlesnake has sensory pits on the head through which it can detect a nearby warm-blooded animal. Even the simplest one-celled animals respond to touch. If a flatworm is touched, it may jerk away or curl up into a ball. It moves away from strong light or from water that is too hot or too cold.

In the warm, muddy rivers of Western Africa there are fish that send out small electric impulses and surround themselves with an electric field. Whenever another fish or other object approaches, the fish is made aware of it by the changes in the charged field. Thus a built-in electric system takes the place of eyesight in the dark waters and keeps the fish informed of its surroundings. Bats emit high-pitched squeaks and use the reflected sound waves to avoid objects and locate prey while flying. Dolphins and whales send out ultrasonic signals and are able to detect objects by reflections of the sound.

Migration and Hibernation

When winter comes to northern or high-mountain regions, animals must find some way to keep warm. Many birds and some mammals seek a mild climate by moving south or to lower elevations. They are said to migrate. Other kinds of mammals (bears and woodchucks, for example) store up fat in their bodies in the fall by eating all they can. Then they curl up in a cave or some other protected place and sleep during the cold period that is, they hibernate.

Most insects die in the wintertime. They leave well-protected eggs which hatch in the spring. Fishes, frogs, and aquatic arthropods and other water-dwelling animals may hibernate in mud or move to deeper water and become inactive.

Living Together in Colonies

Social insects, those living in communities and having differentiated forms or castes, as queens, workers, drones.

Some animals live with others of their own kind. Ants, honeybees and bumblebees, and wasps are called social insects because they live together in highly organized societies.

Some birds live in large colonies. Penguins, anis, and eider ducks are examples. Weaver finches work together to build huge community dwellings.

South American monkeys travel through the jungles in family groups. They scatter while they are searching for food but stay within sight or hearing of one another. Toward evening they regroup and spend the night together. Baboons live in large bands. They cooperate in getting food and post sentries to watch for danger when the group stops.