Friday, Aug. 2, 2002
* Japanese name: Namiuzumushi
* Scientific name: Dugesia japonica
* Description: Flatworms are tiny animals a bit like miniature slugs, about 1 cm long. They have thin, gray-brown bodies with a brain and sense organs at the head end (you can see the eyes in the photo). Flatworms move by gliding -- rather like slugs, but more elegantly. They are almost transparent and quite boring to look at, but scientists all over the world are studying them for two reasons -- their incredible powers of regeneration and their amazing sex lives.
* Where to find them: All over Japan, all year round, in fresh water such as streams, rivers, lakes and rice paddies.
* Food: Flatworms are carnivorous, catching and eating other invertebrates. They may also feed on the remains of dead animals.
* Special features: If you decide to kill a flatworm by cutting it into 200 pieces, you won't have much success. The pieces will grow, and within a couple of weeks there will be 200 flatworms. Regeneration comes from dormant stem cells that are found throughout the body. When the worm is damaged, the cells of the injured area regenerate the appropriate parts, even if this means growing a new head and brain.
Flatworms reproduce in two ways. In the asexual way, the worm splits in half and each half regenerates its missing organs. The way flatworms reproduce sexually is equally unusual. Each flatworm has both male and female sexual organs; they are hermaphrodites. When they mate, each flatworm everts its male organ and approaches its partner. In some species, the worms fence with their penises, before penetrating each other and injecting sperm. Sometimes sperm is digested by the worm, otherwise it swims to the ovaries and fertilizes the eggs. The worm's female organs then form a cocoon of eggs.