It was, however, Sir Philip Sidney's sequence "Astrophel and Stella" (1591) that started the English vogue for sonnet sequences. The next two decades saw sonnet sequences by William Shakespeare, Edmund Spenser, Michael Drayton, Samuel Daniel, Fulke Greville, William Drummond of Hawthornden, and many others. These sonnets were all essentially inspired by the Petrarchan tradition, and generally treat of the poet's love for some woman, with the exception of Shakespeare's sequence of 154 sonnets. The form is often named after Shakespeare, not because he was the first to write in this form but because he became its most famous practitioner. The form consists of fourteen lines structured as three quatrains and a couplet. The third quatrain generally introduces an unexpected sharp thematic or imagistic "turn", the volta. In Shakespeare's sonnets, however, the volta usually comes in the couplet, and usually summarizes the theme of the poem or introduces a fresh new look at the theme. With only a rare exception (for example, Shakespeare's Sonnet 145 in iambic tetrameter), the meter is iambic pentameter.