So sorry. Typo error on day one.
It is chapter 6, not chapter 4.
In the olden days, people only saw how new babies were born. In those days, the Chinese people used the word 牝 (pin) to describe vagina. Today, the younger Chinese do not know what this word means because they use 阴道 （yin dao）instead.
Therefore, the early Chinese inferred that whatever was created in Heaven and Earth (universe is a recent word), must have come out from some kind of a 牝. And this 牝 produced many, many different things. Therefore, they added another word 玄 in front, and bingo, a new phrase 玄牝 was created to describe this some kind of a conduit where all the things existing in Heaven and Earth were produced.
