It cut off my riddle so here it is.
In marble walls white as milk,
Linder with skin soft as silk,
Within a fountain crystal clear,
A golden apple does apperception.
No doors are there to this stronghold-
Yet thieves break in and steal the gold.

This is, in fact, a nursery rhyme - the line "a golden apple does apprerception" is totally incorrect, and the it's "lined," not "linder." The "marble walls," in fact, are describing the shell of an egg.

I learned it as:

In marble walls as white as milk,
Lined with a skin as smooth as silk,
Within a fountain color clear.
A golden sphere doth there appear.
No doors are found in this stronghold,
Yet thieves break in and steal the gold.

The gold is inside the egg - the yolk.