Man's mind stretched to a new idea never goes back to its original dimensions Oliver Wendell Holmes Our current understanding of sex and biological differentiation results from the application of three principal experimental approaches to these subjects: those of the physiologist, the biochemist, and the geneticist. These three approaches are illustrated by the materials presented in the chapters of this volume. Chapters 1-5 emphasize conceptualization of developmental processes, describing systems principally from the standpoint of the physiologist. Structures and functions are defined with...

There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact. Mark Twain The recent explosion in ou. r knowledge of basis physiologic processes, molecular biology, and genetic regulatory mech anisms has resulted, in large measure, from a single concep tual advance: the realization that, at the molecular level, evolutionarily divergent organisms are more similar than different. Thus, in Escherichia coli and Homo sapiens, the enzymatic pathways for the utilization of galactose and glu cose are the same, although more than...