The matter of the different subdivisions of that world interpenetrates with perfect freedom, but there is on the whole a general tendency for the denser matter to settle towards the centre.

The conditions are much like those which obtain in a bucket of water which contains in suspension a number of kinds of matter of different degrees of density.

Since the water is kept in perpetual motion, the different kinds of matter are diffused through it; but in spite of that, the densest matter is found in greatest quantity nearest to the bottom.

So that though we must not at all think of the various subdivisions of the astral world as lying above one another as do the coats of an onion, it is nevertheless true that the average arrangement of the matter of those subdivisions partakes somewhat of that general character.
Astral matter interpenetrates physical matter precisely as though it were not there, but each subdivision of physical matter has a strong attraction for astral matter of the corresponding subdivision.

Hence it arises that every physical body has its astral counterpart.