This preface is addressed to the reader who wishes to inquire into the prevailing concepts, hypotheses and theories about development of sensory systems and wants to know how they are exemplified in the following chapters. I believe that science is hypothesis and theory and that the growth and evolution of any branch of science can be measured by the degree to which its theories have been reified. By that standard, one must conc1ude that developmental neuro biologie is in its infancy. The rapid accumulation of observations which has occurred in this branch of science in the past century leads...