Сефер ха-Бахир (Книга Сияния) 88

1"[The students asked,] ""And what is a Mem?""[Rabbi ___ responded,] ""Do not say Mem, rather water [מים]. Just as these waters are wet, so too the belly is always wet.""[They asked,] ""And why does the open Mem include from masculine and feminine, but the closed Mem [only] masculine?""[He replied,] ""To teach you that the essence of Mem is masculine and its end is open for the sake of the feminine. Just as this masculine does not beget in her opening, so too, the closed Mem is not open.* And just as the feminine gives birth and is open, so too, the Mem is closed and open.**""