The xuanpin (a term derived from the Daode jing or Book of the Way and Its Virtue, sec. 6) is an emblem of the conjunction of the male and female principles. "Mysterious" (xuan) refers to Heaven (Yang), and "Female" (pin) refers to Earth (Yin).
The trigrams within the two circles are Li ☲ (Yang containing True Yin) and Kan ☵ (Yin containing True Yang).
The text surrounding the picture says:
(1) Top: "Chart of the Mysterious-Female".
(2) Right and left of the picture: "Gather the solid [line] from the center in the position of Kan ☵ / Transmute by projection the innermost Yin in the palace of Li ☲." (Two verses from the Wuzhen pian, or Awakening to Reality.)
(3) Bottom: "Valley of Empty Non-Being — Root of Heaven and Earth — Mystery and then again Mystery — Gate of All Wonders". (The last two phrases derive from the Daode jing, sec. 1.)