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Dread tape;The big picture

(Photograph) - hat can these squiggles mean? Are they calling cards in a foreign language? An elegant design for window screens? Banners for an exhibition of eastern art? Actually, these are alive. Those decorative designs are the insignia of remorseless reproduction. This is a tapeworm.

More scientifically, these are mature, hermaphroditic segments. The tapeworms do have a front end, the scolex, which hooks into the intestine of their host and co-ordinates movement. But each proglottid (segment) - and there may be several thousand - is reproductively complete and will release eggs. The intriguing squiggles are male and female organs. In some tapeworms, ripe eggs are released though a pore in the centre of each segment, thence to pass out with the products of the host's digestion. In others, the whole segment is discarded, releasing the egg as it rots away. Eggs go on to hatch in intermediate hosts.

Tapeworms are parasites. Each year, an estimated 40 million humans contract severe diseases from tapeworm infestation. Countless millions of animals also have flat, wriggly worms up to one centimetre wide and up to 10 metres long in their small intestines, sharing their lunch. Despite taking a significant portion of their host's sustenance, tapeworms have no mouths or excretory organs. They feed by absorbing nourishment across their tegument, or membrane. They excrete similarly.

The larvae often live in fleas, which is why tapeworms are a major pest on dogs and cats - and their unsuspecting owners. But they can also hatch in pigs and cattle. They can be avoided by hygiene measures such as fully cooking all meat, washing hands before eating, regularly de-worming pets and keeping fleas down.

If in doubt, see a doctor.

Victoria Neumark.

TURN TO PAGE 42 FOR Ted Wragg'S TEACHING TIPS ON THE BIG PICTURE.

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