Much of the character of organisms is due to various symmetries, radial, bilateral, metameric and so forth, and these symmetries arise, partly at least, from the mode of growth by cell division and the marshalling of groups of cells to the places where they are destined to proliferate.
13), they assume simple forms. We then have AB=DC and AD=BC, and c from the symmetries of the figure it is plain that CJ + JD= AD.
How would you define symmetries? Add your definition here.