Posted: December 18th, 2009 | Filed under: Extra unnatural functions | Tags: earthworm, hydrodynamic mechanisms, nature, pressure, soil, starfish, water column | No Comments »
Hydrodynamic mechanisms are also very good for digging burrows. When tunnelling through moist soil, the earthworm contracts the circular muscles at its front end to the utmost. Thus, its head becomes a kind of a sharp awl (if the soil is dry the worm moistens it). Then it looks for some tiny gap between the particles of soil. If it fails to find one, the worm drives its front end into the earth by delivering blows against it from the inside with the aid of its gullet which is operated by a hydrodynamic mechanism. An increase in pressure from 2 to 14 millimetres of the water column allows it to strike blows with a force of 8.5 grams. As soon as the earthworm succeeds in burrowing itself to some depth, it increases the pressure in the front end, making it swell out and thus widen the burrow. If the soil is not very hard, the earthworm will, by repeating this operation, bury itself in the soil before our very eyes. Still more energetic are sipunculids which, when digging their burrows, develop a pressure of up to 600 millimetres of the water column.
Among the most perfect hydrodynamic mechanisms is the locomotion device found in the Echinodermata which is particularly well developed in the starfish, sea-urchins, brittle stars and various sea cucumbers. The arms of the starfish are permeated with symmetrically radiating grooves filled with a watery fluid. Small branches extending from the grooves enter each of the numerous tube feet located on the under surface of the arms. When the starfish moves, the fluid is forced into the tube feet making them swell out and stretch in the direction in which it is moving; after the tube feet get a foothold by means of the suckers on its arms their muscles contract forcing the fluid from the grooves and thus helping the starfish to crawl forward a little. Then the tube feet detach from the ground on which the starfish is moving, the fluid is forced into them again, and the cycle begins anew. This shows that the heart is not the only pump employed by nature to help the organisms of various animals in performing their most vital functions.
Posted: December 16th, 2009 | Filed under: Hydrostatic skeleton | Tags: body, hydraulics, hydrodynamic mechanisms, Hydrostatic skeleton, nature, pressure, siphon-tube | 1 Comment »
Animals can also make elective use of a hydrostatic skeleton, its main advantage being that it can be created for as long as it is needed. When it is no longer required, the pressure in the system can be reduced so that nothing remains of the skeleton. True enough, the hydrostatic skeleton is not as reliable as a bone one, and, where the supports have to be permanent, the hydrostatic skeleton has given way to more rigid constructions. But for non-permanent skeletons hydraulics has proved more advantageous. Nature has applied this invention throughout the history of the evolution of the animal kingdom, right from the lowest creatures up to the most developed ones, man included. Cavernous bodies employing blood as the working fluid is a good example.
Hydrodynamic mechanisms are still more fascinating. These range from extremely primitive devices to rather sophisticated ones. The most primitive of them include the excretory siphon-tube in bivalve mollusks. These living creatures derive oxygen and food, microscopic organisms and particles of plant and animal matter from the surrounding water, which they suck into the mantle cavity. The water saturated with carbon dioxide and polluted with excretory products is ejected through a special siphon-tube. The mollusk, no doubt, wishes the waste material to be removed far away from its body so that it would not return into its mantle cavity. This explains why the excretory siphon-tube is rather long, though it has no special muscle and cannot stretch. When the shell is closed and water stops moving into the mantle cavity, the siphon-tube contracts, but as soon as the fluid resumes its flow, the siphon straightens and stretches.
The hydrodynamic (water-vascular) mechanisms in the spider’s legs are concerned with locomotion. These eight-legged creatures whose legs consist of six or seven segments flex them, like all animals do, by contracting certain specific muscles, but extend them by increasing pressure within the chitin-clad legs.
Posted: December 14th, 2009 | Filed under: Hydrostatic skeleton | Tags: canvas, cardiovascular system, hydraulics, Hydrostatic skeleton, nature, pumping facilities | 1 Comment »
It was not very good to employ the cardiovascular system to perform secondary functions. But after the pumps and the communicating systems had been invented, nature took a profound interest in hydraulics. To begin with, it seems to have guessed that by forcing liquids into the cavities and interstitial spaces it could considerably contribute to the turgor of the tissue, i. e. impart to the tissue a certain degree of mechanical strength. This is but one step from the foundation of the hydrostatic skeleton.
It sounds funny, but man only began using similar constructions in the 20th century, and they are still not being used on a wide scale. The utilization of compressed air is particularly eflective. Picture in your mind’s eye a column of bulldozers and cross-country vehicles which force their way through the taiga to the projected construction site. Within a few hours the space for builders settlement is cleared. Then not very bulky packages are unloaded from the vehicles.
The pumping facilities are switched on, and about half an hour later a settlement of two-storey canvas houses with inflatable beams and supporting structures has sprung up in the place won from the taiga. Convenient and efficient, this time-saving method of construction is surprisingly reliable. Besides, these canvas houses can also be warm enough if their walls are also made inflatable from two or three layers of rubberized canvas.
Posted: December 14th, 2009 | Filed under: Extra unnatural functions | Tags: blood vessels, body, cardiovascular system, high pressure, horned toads, hypertension, nature, obturator muscle | No Comments »
Nature is always striving to allot an organ certain extra unnatural functions. Although the duties of the cardiovascular system are very specific and highly responsible, it could not avoid this common plight since nature was eager to utilize the pressure in the circulation system.
Hypertension (abnormally high blood pressure) is known to be very dangerous for the organism as it may disturb the blood system and cause damage to the blood vessels. Nature, however, turned this phenomenon to advantage. Thus, the lizards, known as horned toads, inhabiting the deserts of Mexico, use the local hypertension in the blood vessels of the head as a means of defence.
Generally speaking, this phenomenon is not terribly uncommon. When the blood, under abnormally high pressure, enters the crests, spines, and other outgrowths on the head and the body, they expand, straighten out, change colour and make the animal look fearful.
This is not the only means of defence of horned toads. Nature supplied them with a wonderful mechanism: when the lizard is standing at bay, a specific muscle, known as the obturator muscle, presses against one of the major blood vessels, markedly raising the pressure in the blood vessels in the head; it proves too high for the delicate vessels in the nictitating membrane and they rupture squirting blood into the face of a predator. This unexpected shower often makes the intruder take flight. This weapon is operative within the radius of one and a half metres.
The other function of the obturator muscle is connected with moulting. The reptiles continue growing throughout their lives. Horned toads change their skin every year. Casting oil one’s clothes can sometimes be difficult. This is where the obturator muscle comes into play. When the pressure in the head vessels increases, all the blood vessels, major and minor, distend and the head expands, tearing the old skin. When the skin on the head has ruptured, the lizard simply crawls out of it through the newly formed opening.