spin around this garden of hope ;
Tuesday, January 16, 2007 @ 4:45 PM
Leeches are segmented worms; their bodies are divided into 34 segments, with a powerful clinging sucker at each end. The mouth is in the anterior sucker and the anus is on the dorsal surface just in front of the rear sucker.
Respiration takes place through the body wall. Sensory organs on the head and body surface enable a leech to detect changes in light intensity, temperature, and vibration. Chemical receptors on the head provide a sense of smell.
As hermaphrodites, leeches have both male and female sex organs. Like the earthworms they also have a clitellum, a region of thickened skin, which is only obvious during the reproductive period. Mating involves the intertwining of bodies where each deposits sperm in the others' clitellar area. Rhyncobdellids have no penis but produce sharp packages of sperm that are forced through the body wall.
The sperms then make their way to the ovaries where fertilisation takes place. The clitellum secretes a tough gelatinous cocoon that contains nutrients, and it is in this that the eggs are deposited.
The leech shrugs itself free of the cocoon, sealing it as it passes over the head.
The cocoon is either buried or attached to a rock, log or leaf and dries to a foamy crust. After several weeks or months, the young emerge as miniature adults. Studies show that the cocoons are capable of surviving the digestive system of a duck.
Using its many toothed jaws like minute saws, it makes an incision in the skin and excretes a mucous from the nephropores (external openings from the kidney-like organs). This helps the sucker to adhere. A salivary secretion containing the anticoagulant and histamine floods the wound and the leech relaxes its body to allow the blood to be ingested. This mixture allows the blood to flow and also prevents clotting once inside the leech. A bacterium in the gut of the leech assists the digestion of the blood and also prevents growth of other bacteria that may cause the ingested blood to putrefy.