As you will recall from the identically titled segment in our section on the perispirit (see menu bar at left), the union of the soul with the material body of the child to be born, is carried out through the perispirit, which will serve as a tie between the spirit and the matter.  Remember that the spirit is first tied to the embryo through a fluidic bond or "cord", which is actually an extension of the perispirit, that attracts it with an irresistible force, from the moment of conception; as the embryo develops, the fluidic cord shortens, and the perispirit is joined, molecule by molecule, to the embryo.  

In an extremely varied and complex mechanism, either through the action of the reincarnating spirit, or through the action of its spiritual benefactors, the perispirit is reduced, condensed and assimilated to the material molecules.  The perispirit becomes a fluidic mold that acts upon the body in formation, together with the hereditary conditions, the maternal mental influence, and the action of the benefactors that collaborate in the reincarnatory process.