From publisher blurb:
Xenogenesis is the concept of one species giving rise to another. There are at least four forms of xenogenesis, Will, where one creature causes its flesh to mold or spawn another; Alchemy, where the process of creation requires chemical substance and laboratory processes; Natural Laws, where the laws of the universe cause the creation of new life from old; and Blood Auras, where one creature causes another to give birth to a third.
“Xenogenesis in Fantasy Settings” includes guidelines on how to create, use, and incorporate into games the four variations of manufactured creatures and stats for 27 sample monsters.
Material in this publication was written specifically for the "Basic" version of the OGL/d20 system by game developer Derek Holland and can be used as-is or easily adapted for other games using the same core rules.