What is the X in X-mas?
1859, from embryon (see embryo) + -logy. Related: Embryologist (c.1850).
embryology em·bry·ol·o·gy (ěm'brē-ŏl'ə-jē)n.
The branch of biology that deals with the formation, early growth, and development of living organisms.
The embryonic structure or development of an organism.
The study of the embryo; a major field of research in modern biology.