W. Warde Fowler 
Roman Festivals of the Period of the Republic [PDF ebook] 
An Introduction to the Study of the Religion of the Romans

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Mommsen (chron. 13) believes it to have been a Pythagorean doctrine which spread in Southern Italy. Hartmann, on the contrary, calls it an old Italian one adopted by Pythagoras. See a valuable note in Schwegler, Rom. Gasch. I. 561, inclining to the latter view.