To aestivate is to lay dormant for the summer. Aestivation is similar to the familiar hibernation that many animals do, but is carried out by those creatures that don't like hot, dry weather. Such as the snail. Aestivation is not uncommon in animals who live in hot climates, especially those who require a degree of moisture, thus both land and water tortoises frequently retire into cavities of the ground during heat and drought and remain there until the recurrence of the rainy season. Research Aestivate
Byssus are the silky threads by means of which many bivalves attach themselves to a firm surface. The byssus threads are secreted in a gland in the foot which is the homologue of the mucusgland of the snail, and can be speedily renewed if severed. They are seen in very simple form in the common edible mussel (Mytilus), which is always attached to its surroundings by a tuft of golden threads. Research Byssus
In an organism, circulation is the flowing of sap or blood through the veins or channels, by means of which the perpetual and simultaneous movements of composition and decomposition manifested in organic life are carried on. Although Galen, who had observed the opposite directions of the blood in the arteries and veins, may be said to have been upon the very point of discovering the circulation, the discovery was reserved for William Harvey, who in 1628 pointed out the continuity of the connections between the heart, arteries, and veins, the reverse directions taken by the blood in the different vessels, the arrangements of valves in the heart and veins so that the blood could flow only in one direction, and the necessity of the return of a large proportion of blood to the heart to maintain the supply.
In 1661 Malpighi exhibited microscopically the circulation in the web of a frog's foot, and showed that the blood passed from arteries to veins by capillaries or intermediate vessels. This finally established the theory with regard to animals, but the movements of sap in vegetables were only traced with difficulty and after numerous experiments.
Many physiologists were reluctant to ascribe the term 'circulation' to this portion of the economy of plants; but though sap, unlike the blood, does not exhibit movements in determinate vessels to and from a common centre, a definite course is observable. In the stem of a dicotyledonous tree, for example, the sap describes a sort of circle, passing upwards from the roots through the newer woody tissue to the leaves, where it is elaborated under the action of air and light; and thence descending through the bark towards the root, where what remains of it is either excreted or mixed with the new fluid, entering from the soil for a new period of circulation.
In infusorial animalcules the movement of the fluids of the body is maintained by that of the animal itself and by the disturbing influence of nutritive absorption. In the Coelentera (zoophytes, etc) the movement receives aid besides from the action of cilia on the inner walls of the body. The Annelids, as the earth-worm, possess contractile vessels traversing the length of the body. The Insects, Crustaceans, Myriapods, and Spiders have a dorsal tube, a portion of which may be specially developed as a heart. The blood is driven to the tissues, in some cases along arterial trunks, being distributed not in special vessels, but simply through the interstices of the tissues. From the tissues it is conveyed, it may be by special venous trunks to a venous sinus which surrounds the heart and opens into it by valvular apertures. The Mollusca have the heart provided with an auricle and a ventricle, as in the snail and whelk; two auricles, one on either side of the ventricle, as in the fresh-water mussel; or two auricles and two ventricles, as in the ark-shells. Among the ascidians, which stand low in that division of animals to which the molluscs belong, the remarkable phenomenon is encountered of an alternating current, which is rhythmically propelled for equal periods in opposite directions.
All vertebrated animals (except Amphioxus) have a heart, which in most fishes consists of an auricle and ventricle, but in the mud-fishes (Lepidosiren) there are two auricles and one ventricle; and this trilocular heart is found in the amphibians, and in most reptiles except the crocodiles, which, like birds and mammals, have a four-chambered organ consisting of two auricles and two ventricles. In these two last-named classes the venous and arterial blood are kept apart; in the trilocular hearts the two currents are mixed in the ventricle. Research Circulation
Dipsadinae is the 'American Snail-eating Snakes' subfamily of reptiles of the typical snakes family, Colubridae, suborder Serpentes (Snakes). The subfamily contains three genera and about 48 species found in South and Central America within rain forests and montane forests. The members vary in length from 25 to 90 cm, and are highly specialised with long front teeth which are used to extract snails from their shells. Research Dipsadinae
Drilidae is a family of beetles whose male members have fully developed wings and elytra, and female members are like larvae - wingless, with short legs, antennae and a small head. The males frequent flowers while the females are to be found in damp hidden spots, under stones and in snail shells. Research Drilidae
Ianthina (purple shell or violet snail) is a genus of beautiful pelagic gastropods of a violet colour. They float at the surface of the sea, with the thin shells upturned and feed on various kinds of jelly-fish. A special peculiarity is the 'raft', which is attached to the foot, and has the egg capsules suspended from its under surface. This raft or float consists of a mucoid substance, and is filled with air-bubbles, by means of which it sustains the attached animal at the surface of the water. The ancient Tyrian purple dye was obtained in part from these animals. Research Ianthina
Pareinae is the 'Asian Snail-eating Snakes' subfamily of reptiles of the typical snakes family, Colubridae, suborder Serpentes (Snakes). The subfamily contains two genera and about 15 species found in South-East Asia within rain forests and montane forests. The members grow to 90 centimetres in length. The members have a head distinct from the laterally compressed body and have long anterior teeth in the lower jaw. As their popular name suggests, the members of the subfamily feed almost exclusively on snails. Research Pareinae
In zoology, the periwinkle is any marine snail of the family Littorinidae, found on the shores of Europe and eastern North America. Periwinkles have a conical spiral shell, and feed on algae. Research Periwinkle
The snail is an air breathing gastropod mollusc with an external shell. Snails are of world-wide distribution, found everywhere except the polar regions. There are many thousands of species, with more than 120 British species, some terrestrial and some aquatic living in fresh water. There are also marine snails, of which the Periwinkle is a familiar specimen. Snails vary in size from tiny, smaller than the head of a pin, to tropical species with shells more than twenty centimetres long. Snails love damp spots and are most active after rain. In continued dry weather they retire underground or to sheltered spots, close the orifice of the shell with a film or epiphragm of dried mucus, and aestivate (remain dormant) until the damp weather returns. During the winter most snails hibernate.
The great majority of snails are vegetarian, though several British species are more or less carnivorous. Some snails possess a remarkable homing instinct, the common snail (Helix aspersa) returning to the same spot to sleep for the entire course of its life unless displaced by an accident.
Almost all snails are nocturnal, only roaming during daylight in the rain. Snails travel slowly, by way of wave-like ripples in their muscular foot. The lifespan of snails varies greatly with species, most British species living between two and five years. Snails are mostly hermaphrodites, and lay eggs. The edible snail lays eggs about the size of a pea with a white chalky shell. Some large species lay eggs as large as a bird's egg.
All terrestrial snails are edible, and were widely eaten in Britain before the Industrial revolution. Research Snail
The Song Thrush or Mavis (Turdus musicus) is a British bird with brown upper parts, tinged with olive, a throat which is white in the middle, white flanks and abdomen which are spotted with oval dark brown markings. The Song Thrush feeds on worms, insects and snails which it picks up and breaks their shell by dashing the snail against a stone, using the same stone repeatedly returning to it as it finds snails to eat. In the spring caterpillars are also eaten and in summer berries also. The nest is built of grass and twigs, lined with mud and rotten wood. Research Song Thrush
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Aestivate
