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The Hydra was killed by Heracles. According to most traditions, this deed constituted the second of his famous Twelve Labors. When Heracles battled the monster, however, he managed to get around this inconvenience by cauterizing the severed necks with fire so they could not regrow.
The Hydra, also called the Lernean Hydra because it lived near Lerna in Greece , was part of a brood of ancient mythical monsters. Its parents were the creatures Typhoeus and Echidna, and its siblings included other multi-headed beasts, such as Cerberus and the Chimera. The Hydra itself was a serpent with numerous heads the exact number varied in ancient sources. Its blood and even its breath were poisonous. The Hydra was eventually killed by Heracles , who was sent to fight it as one of his Twelve Labors.
Once the monster was finally dead, Heracles dipped his arrows in its poisonous blood; he would go on to use these poisoned arrows in many future battles. Hercules and the Hydra by Antonio del Pollaiolo ca. The Hydra lived in the swamps near Lerna, a town in the eastern Peloponnese.
Ancient authors claimed that the creature haunted a spring named for Amymone, a daughter of Danaus and a lover of Poseidon , until it was finally killed by Heracles. Though the Hydra was as far as we know always imagined as a many-headed creature, there was no consensus as to the exact number of heads or its other attributes and abilities. The earliest known depiction of the Hydra was found on a pair of bronze fibulae decorative brooches or pins made in Boeotia around BCE; it showed the monster with six heads.
Literary representations of the Hydra began to appear around the same time, starting with Peisander in his lost epic the Heraclea late seventh century BCE. However, Peisander failed to specify exactly how many heads the Hydra had. Later poets gave a range of suggestions for the number of heads. This number was probably the most popular one in antiquity.
Vase painting showing Heracles and Iolaus fighting the Hydra, in the manner of the Princeton Painter ca. The Hydra is here depicted with eleven heads—a number not attested in any literary sources. Louvre Museum, Paris, France.
Another important attribute of the Hydra was its ability to regenerate its heads. But by the first century BCE, it was commonly said that the Hydra regrew two 7 or even three 8 heads for every one that was cut off. Taking this ability into account, the Hydra could have started out with any number of heads and then increased them exponentially. The Hydra also exuded deadly poison.
The appearance of the Hydra was even more scattered and inconsistent in the visual arts. On ancient vase paintings, for example, it was not unheard of for the Hydra to be represented with seven, eight, ten, or eleven heads—numbers otherwise unattested in the literary traditions. But these depictions were a later development of the myth, and relatively rare.
Some ancient writers tried to come up with a rational explanation for the myth of the Hydra. Heraclitus, for example, suggested that the Hydra really had only one head, but was accompanied by its numerous brood—that is, the Hydra was really many snakes rather than a single many-headed snake. The Hydra was one of the children born to the monsters Typhoeus and Echidna.
Typhoeus and Echidna were usually represented with serpentine features and many heads—characteristics they passed on to their terrifying offspring. The battle between the Hydra and Heracles was no accident. According to the seventh-century BCE poet Hesiod, the terrible creature was raised by Hera for the express purpose of slaying Heracles, whom she hated as an illegitimate son of her husband Zeus. According to the most familiar version of the myth, Heracles found the Hydra in its swamp near Lerna and attacked it with the help of his nephew Iolaus.
Eventually he realized that he could prevent the heads from growing back by quickly cauterizing the stumps with fire. Thus, every time Heracles cut off a head, Iolaus scorched it with a torch so that it would not grow back. In this article, you will learn about this fantastic creature in detail: by definition, classification, and cellular structure.
I will show you several interesting behaviors when a hydra feeds or move. We will also see what happens to a sick hydra. Finally, you will also learn where and how to collect a hydra for your microscopic project.
Hydras are classified under the phylum Cnidaria and the class Hydrozoa. Examples of Cnidarians include jellyfish , sea anemones , corals , and hydras. They are predominantly marine species, but a smaller number of species including hydras are found in rivers and freshwater lakes. Cnidarians are incredibly diverse.
Examples of Cnidarians include jellyfishes, sea anemones, corals, and hydras. Photo credit: Dr. Sebastian Fraune. Hydras live in all kinds of freshwater habitats, including ponds, ditches, and slow-flowing rivers and streams. They are native to temperate and tropical regions. Hydra usually anchors itself to a substrate like a water plant by its foot. Photo credit: Jan Hamrsky. Yes, hydra has a low tolerance for pollution. Since hydra cannot be found in contaminated water, they can be used as a biological indicator to rank toxicants on the level of a potential hazard.
Their tentacles may extend much longer — some species of green hydra may measure about 5 cm to 20 cm when extended. The body of a hydra may retract while sensing a danger , making the organism appear shorter and rounded. Stentors are almost the largest single-celled ciliates and can grow up to 4 mm. You can see the hydra is much bigger than stentors. A small hydra may look transparent in its tentacles and yellowish in its tube-like body. Hydra oligactis is brown; therefore, also known as the brown hydra Hydra viridissima is commonly called green hydra because of its distinctive color due to the symbiotic green algae Chlorella that live within its body.
Right: Hydra viridissima. Photo credit: Hydra oligactis , Hydra viridissima. Hydra has a tubular body with radial symmetry. The radial symmetry is also a shared feature of the phylum Cnidaria. You can see the body wall of a Hydra consisting of two layers of cells.
Hydra has two main body layers. The outer layer is the epidermis like our skin which can secret a protective layer hydramacin against bacterial infection. Respiration and excretion occur by diffusion through the surface of the epidermis. The inner layer is called the gastrodermis , which lines the stomach.
Between the two layers is a gel-like substance called mesoglea. Modified from Vogg MC. The bottom end of a hydra is secured on the surface by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that accounts for its adhesive properties.
At the free end of the body is a mouth opening hypostome surrounded by tentacles. The mouth is connected to the body cavity. The prey captured by the tentacles will then be engulfed within the body cavity for digestion. Since hydra has only one opening, the waste after digestion will be discharged through the same mouth opening.
Tentacles from 6 to 10 in number radiate outward from the rim of the mouth. These tentacles can be greatly extended at the time of feeding or locomotion. Each tentacle is covered with highly specialized stinging cells called cnidocytes. Cnidocytes contain specialized structures called nematocysts , which look like miniature light bulbs with a coiled thread inside.
Near the outer edge of the cnidocyte is a short hair, called a cnidocil. The cnidocil functions like a trigger to control the firing of a nematocyst. Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release.
These toxins can paralyze the prey. A cnidocyte fires a structure that contains the toxin from a characteristic subcellular organelle called a nematocyst. Left: a cnidocyte at the resting stage. Right: a fired cnidocyte. Hydra does not have a recognizable brain or true muscles, but hydra has a primitive nervous system called the nerve net.
Nerve nets connect sensory photoreceptors light-sensitive and touch-sensitive nerve cells located in the body wall and tentacles. This simple nervous system helps hydra quickly respond to all kinds of stimuli. You can see the hydra has a network-like nerve system. Photo credit: ck Photo credit: U Heidelberg.
Hydras mainly feed on aquatic invertebrates such as Daphnia. While feeding, Hydras extend their body to maximum length and then slowly extend their tentacles. Once fully extended can be four to five times the length of the body , the tentacles are slowly maneuvered around, waiting for contact with suitable prey. Upon contact with prey, hundreds of nematocysts can fire their stings and neurotoxins at the same time. This can paralyze the prey. Within minutes, the tentacles can surround the prey and move the prey into the opened mouth aperture.
The prey will then be engulfed within the body cavity for digestion. Hydra can stretch its body wall considerably in order to digest prey more than twice its size. Since hydra has no anal pore, the indigestible remains of the prey will be discharged through the mouth aperture via contractions.
The mouth disappears after it eats, meaning a hydra regrow a new mouth for each bite. Is that amazing? Some Hydra species like Hydra viridissima can form a symbiotic relationship with green algae Chlorella living within its body. Hydra provides a safe place to live, and green algae synthesize food by photosynthesis in return.
This symbiosis gives a significant advantage to hydras when environmental conditions change food is scarce. In the absence of prey, a green hydra may still be able to survive for about 3 months using nutrients produced through photosynthesis. This allows the hydra to tolerate starvation. Green hydra Hydra viridissima and its symbiotic algae Chlorella sp. Modified from Marinespecies. Typically, a hydra remains attached by the basal disc to some suitable object in the water.
However, occasionally hydra can move quite readily, especially when hunting. Looping is the most common type of walking similar to the movement of a caterpillar.
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