To understand the normal biologic role of reverse transcriptase, Kiessling began to study eggs and early cleaving embryos.

After a decade of debate, and a report prepared under the direction of Mary Warnock, a moral philosopher, Parliament in 1991 set up the Human Fertilization and Embryology Authority, an agency that licenses both fertility clinics and research institutions that study human embryos.

But experts suspect that some scientists, trying to improve the success rate of in vitro fertilization or to fight birth defects, may be quietly studying embryos.

He was owned by a woman named Kirsi Sanai, a Ph.D. scientist who studies embryos.

Scientists could study the cloned animals and embryos that now exist to determine their properties and potential.

He soon passed on to the vertebrates, and studied the amphibians and mammalian embryos.

Studying embryos of modern birds and reptiles, biologists think they have found evidence disputing the prevailing theory that birds descended from dinosaurs.

With no Federal money to pay for the research, studies of in vitro fertilization have been carried out by scientist-entrepreneurs, many of whom left Government laboratories to work on their own, the only way they could study human embryos.

He said he had wrestled with the question of studying embryos and had concluded that because they still had the capacity to divide until they were 14 days old, they had not yet become an individual and therefore could not be construed as a person.

Those divergent views were quickly made apparent when Michael S. Gazzaniga, a professor of neuroscience at Dartmouth College who is on the council, argued that "a rich source for stem cells to be used in research" was jeopardized by a failure to agree on whether federal money could be used to study leftover embryos.