Edited by D. A. Coult, of the University of Liverpool, a new series of paperback monographs was begun in 1966 by Longmans Green and Co., Ltd., and is now being published in the United States by Houghton Mifflin Company. This series like others being presented by other companies, has been stimulated by the impressive growth made by biology in the last twenty-five years and by contemporary advances in physics, chemistry, mathematics, and engineering.