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Sep 27, 2009 Features / Columnists, Interesting Creatures in Guyana
Monkey frogs are a group of tree frogs (Phyllomedusa hypocondrialis, phyllomedusa sauvagii) which are characterized by long limbs and a lack of webbing between their toes. This last trait allows them to grasp branches and to climb trees in the manner of a monkey, hence their name. This frog is a very large tree frog with certain species having the ability to produce hallucinogens in their skin.
They have broad bodies, no identifiable neck, no tail, four legs and have a wide mouth and tiny nostrils on their snout. This frog species has eyes for exceptional vision and it can have either moist, smooth or rough skin. From their movement, vision, breathing, skin, hearing, temperature control, and smell to their strange reproduction processes, these frogs have a ‘lycra’ type skin that protects them from injury and disease.
Though most of them are green in colour some wonderful variations have been spotted. Colours can help warn predators that the frog may be poisonous. And many frogs change the colour of their skin to change their heat absorption rate thus they are able to control their temperature. Also water and other secretions help sustain temperature even as their skin is water permeable; this means it can let water in and out.
Patterned skin can help camouflage the frog, so it sinks into the background, out of the sight of predators. All frogs regularly shed their skin and most eat the shed skin for nutrition and water. In dry environments, some frogs have been known to retain their skin as a cocoon to keep in water.
As in other higher vertebrates, the frog’s body may be divided into a head, a short neck, and a trunk. The flat head contains the brain, mouth, eyes, ears, and nose. A short, almost rigid neck permits only limited head movement. There is no partition in the frog’s coelom as all of the frog’s internal organs, including the heart, the lungs, and all organs of digestion are held in a single hollow space.
The frog’s body is supported and protected by a bony framework called the skeleton. The skull is flat, except for an expanded area that encases the small brain. Only nine vertebrae make up the frog’s backbone, or vertebral column. As in other vertebrates, the frog skeleton is moved by muscles. Skeleton-moving muscles are made of skeletal or “striated” muscle, but the internal organs contain smooth muscle tissue.
The frog’s heart is the only organ contained within the coelom which has its own protective covering. There are two upper chambers of the heart, the right atrium and the left atrium. The heart, however, has only one lower chamber, a single ventricle. Oxygen-laden blood and oxygen-poor blood containing waste gases are present together in the frog ventricle at all times. The oxygen-laden and oxygen-poor bloods, however, do not mix.
Such mixing is prevented by a unique arrangement of the frog’s heart. Instead of “perching” on top of the ventricle, the right atrium dips downward into the ventricle. This causes oxygen-poor blood entering the right atrium to pass all the way down to the bottom of the ventricle. Meanwhile, oxygen-laden blood is received by the left atrium and enters the same single ventricle. The pool of oxygen-poor blood at the bottom of the ventricle holds up the oxygen-laden blood and prevents it from sinking to the bottom. When the oxygen-poor blood flows from the ventricle into vessels leading to the lungs, the oxygen-laden blood tries to “follow” it. The lung vessels, however, are filled with oxygen-poor blood, blocking the oxygen-laden blood and forcing oxygen-laden blood to detour into the arteries. These carry the oxygen-laden blood to the tissues. Frog blood has both a solid and a liquid portion. The liquid plasma carries solid elements such as red blood cells and white blood cells.
The frog is covered by a soft, thin, moist skin composed of two layers, an outer epidermis and an inner dermis. The skin does not merely protect the frog but helps in respiration. An extensive network of blood vessels runs throughout the frog’s skin. Oxygen can pass through the membranous skin, thereby entering directly into the blood. When a frog submerges, all its respiration takes place through the skin. Oxygen is obtained directly from the water.
The frog does not breathe through its skin alone. Adult frogs have paired, simple, sac-like lungs. As in man, air enters the body through two nostrils, passes through the windpipe, and is received by the lungs. The mechanism of breathing, however, is different in the frog from than in man. In humans breathing is aided by the ribs, the diaphragm, and the chest muscles. The frog has no ribs or diaphragm, and its chest muscles are not involved in breathing. A frog may breathe by simply opening its mouth and letting air flow into the windpipe. However, it may also breathe with its mouth closed. The floor of the mouth is lowered, causing the frog’s throat to “puff out.” When the nostrils open, air enters the enlarged mouth. Then, with nostrils closed, the air in the mouth is forced into the lungs by contraction of the floor of the mouth.
The frog’s mouth is where digestion begins. It is equipped with feeble, practically useless teeth. These are present only in the upper jaw. The frog’s tongue is highly specialized. Normally, the tip of its tongue is folded backward toward the throat. From this position the frog can flick it out rapidly to grasp any passing prey. To better hold this prey, the tongue is sticky. Food passes from the frog’s mouth into the stomach by way of the esophagus. From the stomach, the food moves into the small intestine, where most of the digestion occurs.
(Source: Wikipedia – The Free Online Encyclopedia)
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