Proceedings of the National Academy of Sciences of the United States of America. 01/06/98, Vol. 95 Issue 1, p282. 6p. 10 Color Photographs, 4 Diagrams.
Proceedings of the National Academy of Sciences of the United States of America. 10/29/96, Vol. 93 Issue 22, p12496. 6p. 4 Black and White Photographs, 2 Charts, 5 Graphs.