The document summarizes key aspects of comparative embryology in mammals such as the formation of the coelom, types of extra-embryonic membranes, and gastrulation. Specifically, it discusses how the coelom forms from the mesodermal layer and the differences between protostomes and deuterostomes. It also outlines the main extra-embryonic membranes - yolk sac, allantois, amnion and chorion - and their functions in protection and nutrient/waste exchange during development.