A symposium presented on August 26-27, 1957, at the Stanford University joint meeting of the American Institute of Biological Sciences and the Pacific Division of the American Association for the Advancement of Science, and a symposium presented on December 28, 1957, at the Indianapolis meeting of the American Association for the Advancement of Science.
Reprint of the 1958 ed. published by the American Association for the Advancement of Science, Washington as its Publication no. 51.