Head is the term applied to the anterior part of the body of an animal when marked off by a difference in size, or by a constriction (neck). A gradual increase of complexity in the structure of the head is observable as we ascend from the lowest to the highest forms of life. In the Protozoa, Infusoria, and Coelenterates nothing that can be regarded as a head is found, and it is not until we ascend to the worms proper, the articulated animals (crustaceans, myriapods, spiders, and insects), the land and fresh-water gasteropods (snails and whelks), and the cuttle-fishes, that a head proper is found.
The cuttle-fishes have a remarkable cartilaginous box, which, like a skull, protects their anterior nervous ganglia and gives support to the muscles. The head of the vertebrated animals presents a regular series of increasing complexity from the lancelet upwards, and as the anterior nervous mass enlarges, and its ganglia increase in complexity, so do the anterior vertebra change their character; as the brain becomes specialized, so does the brain-case or skull, attaining its highest development in man.
In man, and in the higher vertebrates, the head consists of an upper chamber, lodging the brain, the eyes, and other sense organs, and a lower, lodging the first portion of the alimentarycanal. In proportion as the vertebrates become developed, the brain increases in size, and its position advances anteriorly, until, in man, it comes to overhang the face.
Head is the unit of measurement of cattle. Thus a herd of 100 cattle is referred to as 100 head.
A pearl is a lustrous concretion produced by certain bivalve molluscs (muscles and oysters) and valued as a gem. Pearls consist almost entirely of nacre, which is the substance forming the inner layers of the mollusc shells. Nacre, known as mother-of-pearl, is composed primarily of aragonite crystals. The pearl is an abnormalgrowth resulting from the invasion of the body of the mollusc by a minute parasitic worm (it was previously believed to be invasion by a grain of sand or similar which caused the pearl to be produced), which cannot escape and irritates the mollusc which retaliates by coating the irritant with layer upon layer of nacreous material. Both marine and freshwater molluscs produce pearls, but the most valuable varieties originate in the pearl oyster of the Persian Gulf. The most highly prized pearls are spherical. When a pearl that has been cut from the shell presents a hemispherical surface, it is sometimes called a bouton pearl. If a solid pearl has an irregular shape, having grown over a rough object, it is known as a baroque pearl. In the jewellerytrade, pearls are commonly known as pear, bell, or drop, according to the shape. Pearl coloration varies widely, the most prized shades being white, black, rose, and cream. River pearls are produced by freshwater mussels in various parts of the world. China is the principal trader in river pearls. Natural, spherical pearls have been cultured successfully since 1920. In this process a mother-of-pearl bead, from three-quarters to nine-tenths of the diameter of the desired product, is introduced into the
pearl oyster. Over a period of years the oyster deposits layers of nacre around the bead. Cultured pearls are not easily distinguished from genuine pearls except by an expert. The technique of producing spherical cultured pearls was developed in Japan, and the culturing of pearls is a major Japanese industry - a small bead of mother of pearl being inserted into the oyster which grows the pearl around the bead. Artificial pearls, in contrast to cultured pearls, are entirely man-made, largely of glass. Research Pearl
Barnacle is the popular name of a family (Lepadidae) of marine crustaceous animals, order Cirripedia. They are enveloped by a mantle and shell, composed of five principal valves and several smaller pieces, joined together by a membrane attached to their circumference; and they are furnished with a long, flexible, fleshy stalk or peduncle, provided with muscles, by which they attach themselves to ships' bottoms, submerged timber, etc. They feed on small marine animals, brought within their reach by the water and secured by their tentacula. Some of the larger species are edible. According to an old fable these animals produced barnacle geese. Research Barnacle
The beaver (Castor) is the only genus of the family Castoridae. The family contains a single genus, Castor, with two species: Castor canadensis, found in the New World, and Castor fibre, found in the Old World. Both species are semi-aquatic rodents noted for the building of dams. The two species differ chiefly in the shape of the nasal bones and are so much alike that some authorities consider them to be varieties of the same species. They are large rodents; the average adult beaver weighs about 16 kg, but specimens as heavy as 40 kg have been found, and some extinct beavers were almost bear- like in size. The beaver is usually about 76 centimetres long and stands less than 30 centimetres high, with a broad, flat, scaly tail about 25 centimetres long.
The body is plump, the back arched, the neck thick, the hind feet webbed, and all the digits clawed. The fur is usually reddish- brown above and lighter or greyish below. The eyes are small and the nostrils closable. The skull is massive, with marked ridges for fixing the muscles that work the jaws. The two front teeth on either jaw are like those of other rodents, wearing away more rapidly behind so as to leave a sharp, enamelled chisel edge. With these the beaver can cut down large trees. It usually selects trees five to 20 centimetres in diameter, but it can fell trees with diameters as large as 76 cm.
Beavers have a pair of anal scent glands, called castors, that secrete a musk-like substance called castoreum, probably for marking territories. The animals tend to be monogamous and have a life span of 20 years or more. The female has one litter a year, usually of two to four young.
Beavers are social animals and in areas where food is abundant and the locality secluded, the number of families in a beaver community can be rather large. The so-called beaver lodge is a unique structure. Three distinct kinds exist, their differences depending on whether they are built on islands, on the banks of ponds, or on the shores of lakes. The island lodge consists of a central chamber, with its floor a little above the level of the water, and with two entrances. One of these, the 'wood entrance', is a straight incline rising from the water, opening into the floor of the hut. The other approach, the 'beaver entrance', is more abrupt in its descent to the water.
The lodge itself is an oven-shaped house of sticks, grass, and moss, woven together and plastered with mud. The room inside is carpeted with bark, grass, and wood chips, sometimes with special store rooms adjoining. The pond lodge is built either a short way back from the edge of the bank, or partly hanging over it, with the front wall built up from the bottom of the pond. The lakelodge is built on the shelving shores of lakes. Dams are used by beavers to widen the area and increase the depth of water around their homes and are constructed either of sticks and poles or more firmly and solidly of mud, brushwood, and stones. As time goes by the beaver repairs and adds to the dam. Floating material lodges there, and vegetation growing on the top adds its roots to the strength of the dam. Frequently the beaver builds a smaller dam downstream in order to back up some water against the original dam and thus decrease the pressure of water on it from the other side. The dams are about 1.5 metres high, usually more than three metres wide at the base, and narrow at the top. A beaver dam more than 300 metres long was found in Rocky Mountain National Park, Colorado.
Beaver ponds eventually fill with sediment, and the animals move to a new location. The abandoned area becomes good meadowland. Beaver dams also help control runoff. Although the beaver is a powerful swimmer, it has difficulty dragging over the ground the logs and branches it needs for building and for food. Colonies of beavers therefore often dig canals from the pond to a grove of trees. Such canals are up to one metre wide and deep and often a few hundred metres long. The timber is then readily floated down the canal toward the pond.
Beavers have long been exploited for their fur, and for many years during the 18th and 19th centuries hundreds of thousands of beaver skins were exported to Europe from North America annually. The animals were also sometimes destroyed because of the damage they did to forests and the flooding occasionally caused by dams. Ceaseless slaughter led to near extinction of beavers in both Europe and North America. The beaver is almost extinct in Europe, but is becoming re-established in Canada and in protected areas of the USA. Research Beaver
The blindworm or slow-worm (Anguis fragilis) is a reptile, forming a connecting link between the lizards and the snakes, perfectly snake-like in form, having no appearance of external limbs, though the bones of the shoulders and pelvis exist in a rudimentary form. They are about 30 cm long, and of nearly equal thickness throughout. Its eyes, though brilliant, are small, and hence its common name. It is common in Great Britain, and is spread over almost the whole of Europe, Western Asia, and Northern Africa. It is perfectly harmless, living upon worms, insects, and snails, and hybernating during the winter. It receives its specific name of fragilis from the fact that when frightened it stiffens its muscles to such an extent, and becomes so rigid, that its tail may be snapped off by a slight blow. Research Blindworm
The frilled lizard (Chlamydosaurus Kenti) is a reptile of the lizard family Agamidae found in Australia. It grows to about 90 centimetres in length and receives its name from the presence of a large expansion of the skin at either side of the neck, the two halves meeting at the throat. This frill is notched at the edge. has special supporting cartilages, and by means of muscles can be folded or expanded at will. The lizard walks on its hind limbs, having the fore limbs hanging down. Research Frilled Lizard
Frog is the common English name of a number of animals belonging to the class Amphibia, having four legs with four toes on the fore feet and five on the hind, more or less webbed, a naked body, no ribs, and no tail. Owing to the last peculiarity frogs belong to the order of amphibians known as Anura or tailless Amphibia. The tongue is fleshy, and is attached in front to the jaw, but is free behind, so that the hinder extremity of the tongue can be protruded.
Frogs are remarkable for the transformations they undergo before arriving at maturity. In the spring the spawn is deposited in ponds and other stagnant waters in large masses of gelatinous matter. These masses, with black globules scattered through them, soon manifest change, and after a time the young escapes as a tadpole, as an animal with short body, circular suctorial mouth, and long tail, compressed from side to side. Gillsproject on either side of the head from a cleft which answers in position to the gill opening of fishes. The hind limbs first appear as buds, later the fore limbs project, the gills disappear, the lungs becoming more fully developed; the tail gradually shrinks and disappears, and the animal, which was at first fish-like, then closely resembled a newt (or tailed Amphibian), finally assumes the adult or tailless form.
The mature frog breathes by lungs, and cannot exist in water without coming to the surface for air. The only British species is the common frog (Rana temporaria), but the tribe is very numerous, other varieties being the edible frog (Rana esculenta) of the south of Europe, eaten in France and South Germany, the hind quarters being the part chiefly used; the bull-frog of America (Rana pipiens), 8 to 12 inches long, so named from its voice resembling the lowing of a bull; the blacksmith frog of Janeiro; the Argus frog of America, etc. Of the tree-frogs most belong to the genus Hyla. Frogs swim with rapidity, and move by long bounds, being able from the power of the muscles of their hind-legs to leap many times their own length. Research Frog
The Glass Snake is a lizard of the genus Ophiosaurus which resembles a snake in form and reaches a length of one meter. The joints of the tail are not connected by caudal muscles and so the tail is very brittle and joints break off when the animal is even slightly irritated. Research Glass Snake
The Greyhound is a variety of dog distinguished by a greater length of muzzle than any other; very low forehead, short lips, thin and long legs, small muscles, contracted belly and semi pendant ears.
There are several varieties, as the Irish greyhound, the Scottish, the Russian, the Italian, and the Turkish. The common greyhound is of an elegant make of body, and is universally known as the fleetest of dogs. A good hound has a fine, soft, flexible skin, with thin, silky hair, a great length of nose, contracting gradually from the eye to the nostril, a full, clear, and penetrating eye, small ears, erect head, long neck, chest capacious, deep, but not wide, shoulders deep and placed obliquely, ribs well arched, contracted belly and flank, a great depth from the hips to the hocks of the hind-legs, fore-legs straight, and shorter than the hinder. The name appears to have no reference to the colour, but is derived from the Icelandic grey, a dog.
Greyhounds were originally used for coursing, for which their peculiar shape, strength, keenness of sight and speed make them exceedingly well fitted, but are now bred for racing, being the fastest running dogs. As a pet Greyhounds are very gentle and affectionate - but should be kept away from small mammals such as pet rabbits - but require wide open spaces to run about in. Research Greyhound
The horse (Equus caballus) is a hoofed, odd toed grass eating mammal of the family Equidae subdivision Perissodactyla (odd-toed); characterized by an undivided hoof formed by the third toe and its enlarged horny nail, a simple stomach, a mane on the neck, and by six incisor teeth in each jaw, seven molars on either side of both jaws, and by two small canine teeth in the upper jaw of the male, rarely in the female.
There are a number of varieties of horse, popularly known as breeds. The adult male horse is called a stallion, the adult female a mare. A stallion used for breeding is known as a stud. A castrated stallion is popularly called a gelding. A young horse is called a foal, with a male foal being called a colt and a female foal being called a filly.
Horses are among the best adapted of the 'flight' mammals. They have very large eyes capable of seeing in two directions at once, ears which can rotate through 180 degrees and judge distance to a perceived sound, and can reach a speed of 30 mph from a standing still position in less than one second. The horse has a very large heart and enormous lungs powering very large rear leg muscles which allow it to run very fast to escape danger. The horse's long head allows it to graze and see over the top of the grass at the same time, keeping watch for approaching danger. The horse's tail is used as a rudder to help with stearing when running fast, and also as a fly-whisk to whip away flies and other irritations.
When bored or agitated, horses' paw the ground with their rear leags. Stallions fight with their front legs and also bite, trying to ham string their opponent. When a horse wants to harm an opponent, or person, they use their front legs. The rear legs may be used to brush away irritations, and while powerful and dangerous are not used with the intention of causing real harm. War horses, used by mounted soldiers in the Mediaeval period, were trained to attack the enemy and would bite the face off foot soldiers who got close. Research Horse
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Pearl
