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Friday, March 29, 2002

ANIMAL TRACKER

Earthworm


* Japanese name: Aka mimizu
* Scientific name: Lumricus rubellus
* Description: An earthworm's body consists of a tube within a tube. The inner tube is a digestive tract, the outer is segmented and muscular. Between the two are reproductive organs, and running the length of the body is a simple nervous system. At one end is a head, at the other, an anus. On each segment of the outer tube are two pairs of tiny bristles, which the worm uses for crawling -- or for gripping onto the walls of its burrow if a bird tries to pull it out.
* Where to find them: In soil and decaying plant matter, all over Japan. Different species of earthworm live in different parts of the soil, and some (night crawlers) come out at night to feed on plant debris.
* Food: Plant matter. Earthworms process huge amounts of plant litter, converting it into rich topsoil full of nutrients, which plants use to grow. In 1881, Charles Darwin said, "It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures." That's because without earthworms, nutrients in soil would quickly be lost. Worms excrete "casts" of soil, which retain soil nutrients and improve the soil structure.
* Special features: Contrary to popular belief, if you chop an earthworm in half, you don't get two new worms. The nerve cord ends with a "ganglion," a primitive brain, at the head end. Only the bit with the brain survives when a worm is chopped in half by a bird or an inquisitive child. Earthworms often have a "saddle" halfway down their bodies. This looks like a scar but isn't -- it's where baby worms come from. Earthworms are hermaphrodites, which means that male and female sexual organs occur in the same animal. When they reproduce, two worms coil around each other and both animals transfer sperm into the saddle of the other. Eggs are fertilized in the saddle, which becomes a cocoon for the developing eggs. After a few weeks, the cocoon/saddle is slipped off, like a ring from a finger, and left under the soil. The young worms hatch out from it.



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