Complex sentence: It featured two different designs on its reverse during its one hundred years in circulation: from 1860 until 1936, the image of Britannia; and from 1937 onwards, the image of a wren.
Split into simpler sentences: It featured two different designs on its reverse during its one hundred years in circulation. From 1860 until 1936 the image of Britannia, and from 1937 onwards the image of a wren.