This episode explains the order of the Strunk readings and the numbering system used in each title.   

Description Example:  

Part 4: The Baroque Era, Imitation and Expression, Reading 107: Jacopo Peri, Preface to The Music for Euridice.   

In the title of the episode, this would be labeled "4.107" because of the reading being in the 4th part and the 107th episode.