Here are the recent investigations of several distinguished biologists originally presented at the Fourteenth Symposium of the Society for the Study of Development and Growth. New tools and methods are used as they examine a wide range of cellular activities at various levels of plant and animal life. Originally published in 1956. The uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.