This volume continues the custom of addressing developmental mechanisms in a variety of experimental systems by offering timely reviews and incisive analysis of key research in developmental biology. The conceptual sequence of topics begins with cell cycle regulation during development and differentiation, continues with the role of the epididymis and with sperm competition, gastrulation, and embryonic stem cells, and concludes with considerations of differentation in muscle cells and neurons. This volume not only is valuable to researchers at the forefront of animal development, but also is a friendly introduction to students and professionals who want an introduction to cellular and molecular mechanisms of development.