This legend may be familiar to you, as it was in the books listed at the bottom of this page, however it is a legend of the Great Goddess from Italian Witch lore.
And when Diana saw that the light was so beautiful, the light which was her other half, her brother Dianus, she yearned for it with exceeding great desire. Wishing to recieve the light again into her darkness, to swallow it up in rapture, in delight, she trembled with desire. This desire was the dawn.
But, Dianus, the light, fled from her, and would not yield to her wishes; He was the light which flies into the most distant parts of heaven, the mouse which flies before the cat.
Then Diana went to the Fathers of the Beginning, to the Mothers, the Spirits who were before the first spirit, and lamented unto them that she could not prevail with Dianus. And they praised her for her courage; they told her that to rise she must fall; to become the chief of goddesses she must become a mortal.
And in the Ages, in the course of Time, when the World was made, Diana went on Earth, as did Dianus, who had descended, and Diana taught Magick and sorcery, whence came witches and Magickians, and all that is like man, yet not mortal.
And it came thus that Diana took the form of a cat. Her brother had a cat whom he loved beyond all creatures, and it slept every night on his bed, a cat beautiful beyond all other creatures, a fairy; he did not know this.
Diana prevailed with the cat to change forms with her; so she lay with her brother, and in the darkness assumed her own form, and so by Dianus became the mother of Aradia. But when in the morning he found that he lay by his sister, and that light had been conquered by darkness, Dianus was extremely angry; but Diana sang to him a spell, a song of power, and he was silent, the song of the night which soothes to sleep; he could say nothing.
So Diana with her wiles of Witchcraft so charmed him that he yielded to her love. This was the first fascination; she hummed the song which was as the buzzing of bees, and the spinning of the wheel; the spinning wheel spinning life. She spun then the lives of Men, and all things were spun from the wheel of Diana. And it was Dianus who turned the Wheel.
Books
Ways of the Strega, by: Raven Grimassi This is where I got this Legend/Myth word for word. This book is published by Llewellyn and is $20. Order your copy of this book at 1-800-THE MOON
Mastering Witchcraft, by: Paul Huson
Printed in 1970 and one can get copies from Abyss Dist. In this book there is a more generalized version of the Legend of Diana with a few additions.
Aradia-Gospel of the Witches, by: Charles Godfrey Leland
First printing was 1890's or early 1900's, still reprinted and distributed I last heard by Abyss in Massachuesetts. Legends are in this book I heard.