Proceedings of the National Academy of Sciences of the United States of America. 07/07/98, Vol. 95 Issue 14, p8351. 6p. 16 Black and White Photographs, 2 Diagrams, 2 Charts.
Proceedings of the National Academy of Sciences of the United States of America. 02/17/98, Vol. 95 Issue 4, p1432. 6p. 14 Black and White Photographs, 2 Graphs.