[cf. Gabler 20: 6-8; 1922 24:6-9]
Stephen’s student doesn’t seem to have studied very hard and can’t answer the question. His memory fail leads to Stephen’s mental departure, the first of many instances in this chapter where Stephen’s mind wanders away from his job and surroundings, a clear indication of his disengagement with his work. As the narrative voice here seems to unambiguously link to Stephen’s consciousness, Stephen’s departures disconnect us as readers from the narrative events as well.
With the words, “Fabled by the daughters of memory,” Stephen starts thinking of William Blake, British artist/poet/mystic of the Romantic age, who is pictured, suddenly, on the wall of the classroom (which is apparently changing with Stephen’s consciousness). In A Vision of the Last Judgment (1810) Blake writes of the material world as false reality, and thus considers history a fable, a story people make up to teach societal lessons, but one that does not chronicle real events. We see that Stephen cannot agree, much as he might like, as he is unhappily beholden to the material circumstances of his life. (Note the downcast tilt of his head.)
The daughters of memory, as classicists know, are the nine muses of Greek mythology.