Proceedings of the National Academy of Sciences of the United States of America. 05/26/98, Vol. 95 Issue 11, p6198. 6p. 16 Color Photographs, 3 Diagrams.
Proceedings of the National Academy of Sciences of the United States of America. 03/31/98, Vol. 95 Issue 7, p3758. 6p. 3 Black and White Photographs, 7 Diagrams, 2 Charts, 1 Graph.