My Science School

      A hermit crab changes its shell when it has grown large enough to need a bigger home. This type of crab has a soft abdomen or “tail”, which is folded up under the body, but it is not protected by a shell of its own as are most other crabs. Instead, the hermit uses empty snail shells as portable shelters, often having to fight with another crab for possession of an attractive home. Sometimes the home seeker pulls out of the original occupier, eats it and then takes over the shell.

    One of the claws of the hermit is larger than the other. The crab uses this to stop up the entrance after withdrawing into the shell. The last two legs on its abdomen have roughened pads which grip the inside of the shell and hold the body in position. The crab has a spiral-shaped abdomen and moves in and out of its shell with a spiral movement.

    One kind of hermit occupies a sponge which conveniently grows at the same pace as the crab. Sometimes sea-anemones enter into partnership with hermit crabs and take up residence on top of the shells. The crab provides the sea-anemone with transport and in return, receives an extra shield against attack.

          The song of the birds at dawn has given pleasure to millions of people and has been celebrated in poetry and prose for many years. The most usual explanation given in the Middle Ages was that the birds sang each day in praise of God and the beauty with which he had clothed the world. More recently, there was the feeling that the birds sang joyously to welcome the rising of the sun, which meant food, warmth and activity.

          However, scientists now think that the dawn chorus is made up of the warning signals of each bird as he re-establishes his territory for courtship, nesting and food getting is the first step in the breeding cycle and the area is defended against competing birds of the same species by a warning song, although seldom by actual fighting. A robin, incidentally, has a particularly strong sense of territory.

          African elephants have larger ears than Indian, or Asiatic, elephants because they live in hotter conditions and are bigger and more aggressive and active. The huge ears of the African elephant, sometimes three and a half feet wide, enable it to hear more acutely. When the animal charges it fans out it ears, augmenting its terrible appearance and striking fear into the heart of ay enemy.

        The ears also present a large surface for losing body-heat. Africa can elephants, which are at a disadvantage in the heat because of their large size, wave their ears to keep cool and to chase away flies. The African elephant is the biggest and noblest of land animals, reaching a height of 11 feet and a weight of nearly six tons.

        The Asiatic elephant is smaller. It inhabits the forests of South-east Asia from India to Ceylon and Borneo. It does not like heat and seeks the deep shade of the forest.

            A chameleon will change color when it senses danger. This remarkable member of family can change color to match its background or, at least to become almost unrecognizable.

            The ranges of color and patterns of the various species differ widely, but most chameleons can become yellow or cream, green or dark brown. They can also adapt spots either dark or light depending on the color of the ground.

            Apart from its response to danger, the chameleon will change color according to the light and temperature. This mechanism is controlled from the nervous system and involves the dispersion or concentration of color pigments in the creature’s skin.

          Group of elephants have been found buried together both in Africa and Asia. The nearness of the animals to each other may be no more than a coincidence. The areas may be no more than sites, since elevated and dried, where elephants have been drowned in   bags or while crossing river.

           However, many people will argue that old elephants, when their end is near, resort to their legendary “graveyards”. The discovery of the remains of a solitary elephant is rare. On the other hand a body in elephant country would usually soon disappear owing to the activities of natural scavengers.

           Most experts will accept that there is much truth in the old saying “An elephants never forgets”. It does have a retentive memory. Also, when an elephant is dying it is not uncommon for members of the herd gather round and try to revive it. When all hope is lost they encircle their relation as if in mourning at a funeral.

            Butterflies and moths were first classified by the great Swedish botanist Carl von Linne (1707-78), generally known as Carolus Linnaeus. His method, which applied to plants and all living things, was the binomial system. This meant the each insect was given two scientific and internationally recognized names: the first is a generic name denoting the genus or group to which the subject belongs; the second is a specific epithet indicating the species within the group.

            Similarly we all have surnames and forenames. But, in the case of the Linnaean system, Latin or Greek words are used to ensure uniformity regardless of the expert‘s native language. The first or generic name is spelt with a capital letter, but the second name usually begins with a small one.

               Linnaeus published more than 180 scientific works, some of the most important ones after he left Sweden for Holland, where he studied medicine. After visiting England and France he returned to Sweden, where he was given the chair of botany at Uppsala University.

             Bees swarm in late spring in search of new home. During the winter the queen bee begins to lay her eggs and the colony sets about rearing its young. As the weather becomes warmer and the early flowers appear, the raising of young bees increases rapidly.

              By the end of spring the colony has become so overcrowded that a large number of the bees, including the old queen, leave the hive and establish a new queen emerges who will experience the same swarming instincts the following year. And so the cycle of activity goes on.

               Under water, frogs breathe through their skins. A frog is an amphibian. That is o say it lives both on land and in water. It has lungs, but it has no ribs and therefore cannot expand its chest and suck air into its lungs as do reptiles, birds and mammals. On land air is drawn in and out of the frog’s nostrils, which have valves in them, by pulsations of the floor of the mouth. The air is forced in and out of the lungs by contraction of the throat and body muscles. A frog’s mouth is always kept tightly closed and the   pulsations of throat vary from 120-140 a minute.

               Even on land the skin plays a greater part in breathing than the lungs. However, air can be absorbed only through a moist skin. If the skin becomes too dry, the frog will die. Therefore the skin contains glands which secrete a clear mucus or smile whose function is to keep the skin moist and supple. The skin absorbs water as well air, for frogs do not drink.

                Frogs are cold-blooded. That means they are as warm or as cold as the air or water surrounding them. In winter they hibernate under water, where their body temperature fails, their bodily functions are kept at a minimum and breathing is carried on entirely through the skin.

            A caterpillar starts to become a butterfly as soon as it enters the chrysalis stage, by wrapping itself in cocoon. During this phase, known as pupation, the insect gradually develop all the butterfly characteristics, including wings. For some butterflies the transformation may be completed in one or two weeks. But others need many months before they are ready to leave the cocoon and     fly away.

            From the time it is hatched to the time it starts the pupation stage, a caterpillar or larva does little more than eat, grow larger and moult several times. This larval stage varies according to the species. Small caterpillars will complete their development in a week but some large varieties will take us two years or more.

            When this period is over the caterpillars spins a cocoon under a leaf or even underground, and enters it to begin the transformation. Many cocoons are of silk.

The sweet scent of flowers is designed to attract insects who seek food in the shape of pollen and the fragrant-smelling nectar. This nectar is a solution of sugars produced in little sacs called nectarines at the base of the flower petal.

     The insects have a part in the process of fertilization. Almost all plants perpetuate themselves by means of sexual reproduction, during which a male reproductive cell or sperm fuses with female reproductive cell or egg.

     When bees or other insects visit flowers in search of the sweet-smelling nectar, parts of their hairy bodies become dusted with pollen which contains the male reproductive cells. This rubs off on the flower’s carpels which contain the egg or ovule.

Insects seem to be strongly attracted by sweet scents. In fact, some flowers, such as the meadow sweet, are so highly scented that insects are attracted to them although they have no nectar to offer. Most insect-pollinated flowers have evolved wonderful devices for guiding the movements of that pollen is dusted over the insect’s body

Reindeer moss is a species of lichen so called because it is the staple winter food of reindeer (and caribou) in Arctic and Sub-Arctic regions. The animals reach the plant by scraping away the snow with their feet. But Plant growth in those cold northern lands is so slow that the lichen can take more than 30 years to recover after the reindeer have grazed. These domesticated herds therefore have to travel long distance in search of food, and the Laplanders of northern Scandinavia, who depend on the animals for their livelihood, must travel with them.

      Fortunately, reindeer moss is especially abundant in Lapland, although it also grows extensively in much of northern Europe, the tundra (or treeless plains) of Siberia and the barren expanses of Arctic America.

     During the short summer the reindeer are able to feed on herbage and shoots then accessible in the valleys. These versatile animals provide the Laplanders with meat, milk, cheese and the raw materials for clothing, shoes and tents. They are also a means of transport.

     Reindeer moss is sometimes eaten by human beings, after being powdered and mixed with other food. But it leaves a slightly burning sensation on the human palate. This bluish-grey plant grows erect in tufts, and is remarkable for its many branches, which, strangely, resemble a deer’s antlers.

 

 

The first zoo was formed in China in the 12th century B.C. But it was not called a zoo. When, the ancient Chinese king who started it, wanted to collect different types of animals from all over his empire. He kept them in what he called a “garden of intelligence”, near his palace.

      Some of the largest zoos are in North America. There are big ones in the Bronx, New York City, and in Washington and San Diego.

Million of birds of many different varieties migrate at the end of summer. With unfailing regularity they leave the regions where they were born to fly to warmer climates for the winter. The following springs they return to their breeding grounds.

       Each year these migratory birds travel as much as 20,000 miles, finding their day back on time with extraordinary precision. Some travel as individuals.

     Migration is triggered off by the length of daylight, which apparently affects the birds’ nervous systems. When the days get shorter the birds receive the signal to leave for their warmer winter grounds, and, when the daylight increases to a certain level, they receive another signal to return home.