This document discusses sexual reproduction in animals. It differentiates between internal and external fertilization, and describes three types of embryonic development: oviparity, viviparity, and ovoviviparity. External fertilization occurs outside the female body, while internal occurs inside. Embryonic development can involve laying eggs (oviparity), giving live birth after eggs develop inside the female (ovoviviparity), or giving live birth with the embryo nourished by a placenta (viviparity).