LONDON.- Behind the controversial traveling corpse show, "Body Worlds", opening in the Atlantic Gallery this week, lies a morbid international trade in cadavers - some believed to be from prisoners, homeless people and the mentally ill. The exhibition, expected to attract thousands of visitors, is the idea of German scientist Professor Gunther von Hagens and displays 25 corpses and scores of other organs preserved through a 'plastination' technique. The corpses are skinned and their insides exposed. The procedure is legal, but raises the possibility that people who donated their bodies in the cause of medical science could have ended up having their organs displayed in an art gallery. All of the 'whole body' exhibits were donated to Von Hagens by the deceased for exhibition. Von Hagens said he tried to be as careful as possible when buying specimens from medical or museum collections, to avoid ethical problems. The buying and selling of donated corpses and body parts, from private donations or medical collections, is legal in many countries.