What metaphors are used in Darwin in 1881 by Gjertrud Schnackenberg?

In lines 100- 108, the poet describes Miranda and Ferdinand are the "two lovedazed heirs / Who fiddle with the tiny pairs" of chess pieces, in particular the king and queen. As children of royalty, they will one day "turn, themselves, into a king and queen," but what they leave behind are "numberless / Abstract unseen / Combinings on the silent board." This metaphor refers literally to the countless number of moves that can be made in a game of chess but that are never made before the game ends and figuratively to the different combinations of species that never occur in life because of the process of natural selection.