In the top three pictures, Stephen looks out to sea while Mulligan goes down the stairs, reciting a Yeats poem. In the bottom two frames, a voice–presumably inside Stephen’s head, mashes together the poem and his perception of the sea. It’s another example of the “Uncle Charles Principle,” where a voice that is ostensibly the narrator’s takes on the personality and knowledge of an individual character.
Also important to note that if we are inside Stephen’s head here, at least partly, that Stephen is beginning to work on a poem. His mind has left the conflict with Mulligan and has begun to shape, to try to capture in words, a visual impression.
The reference to “lightshod hurrying feet” sounds like a reference to the god Mercury, who, in the Odyssey, is described several times as running over the surface of the ocean with his winged sandals, on his way to deliver messages to mortals.