Caterpillars weave cocoons, polliwogs form from cells; eventually the cocoons break open to produce moths, the cells develop to produce frogs.
What I realize as I observe this is the Tao of liberative transformation of the spiritual embryo.
Those who cultivate reality assemble the five forces, join the hundred spirits, merge with the ultimate; one energy coalesces, whole and pure, not consciously cognized. Now the spiritual embryo has form, like when the caterpillar weaves its cocoon or the polliwog forms its cell.
Store the spirit and energy away in mystical darkness, and the bit of spiritual root will grow from faintness to clarity,
from softness to strength. When the process is complete, suddenly you will break through space to reveal the pure spiritual body, leaping beyond the worlds. This is like when the caterpillar, having transformed into a moth. Breaks out of its cocoon and flies away, or like when the polliwog becomes a frog and leaps. There is a body beyond the body, another world.
Therefore the aftermath of accomplishment of the Way is sometimes referred to as developing the power of flight, and sometimes called shedding the shell and becoming real. These expressions mean that you reproduce a real body inside your physical body. This real body is inherent in everyone, but people are fooled by the objects of their senses, deluded by illusory appearances, so they do not recognize the real body, even though it is right there.
Anyone who can recognize the real body and earnestly cultivate it can produce substance where there was none, produce form where there was none, undergo liberative transformation and become an immortal with an indestructible body.
Awakening to the Tao Liu I-Ming translated by Thomas Cleary p. 76-77