Having listened to Mulligan's clowning about old Mother Grogan making water, Stephen hypothesizes that she "was, one imagines, a kinswoman of Mary Ann." Mulligan picks up on the allusion and is soon belting out a song that he and Stephen both know:
Slote notes that "hising," according to the OED, means "to lift, especially to raise a sail." Given the lifting of skirts, and the link with Mother Grogan, the omitted line must have something to do with urination.
For old Mary Ann
She doesn’t care a damn,
But, hising up her petticoats...
Gifford and Seidman describe "Mary Ann" as “An anonymous bawdy Irish song.” They note that the only printed version cleans up the story of Mary Anne—a young woman who is quite charming “Though in build, and talk, and manner, like a man.” A bawdy version located by Mabel Worthington, however, concludes with a line that perfectly completes Mulligan’s quatrain: "She pisses like a man."
§ In Proteus, Stephen recalls the third line of the quatrain just after urinating into a rising tidepool. Under the surface of the moving water, he sees "writhing weeds lift languidly and sway reluctant arms, hising up their petticoats." In Circe "a standing woman, bent forward, her feet apart, pisses cowily" in the street, her action echoing the musical example of Mary Ann. In this episode Bloom also imagines the reverse: how he once lifted "billowy flounces, on the smoothworn throne," in the interests of "Science. To compare the various joys we each enjoy. (Earnestly.) And really it's better the position... because often I used to wet..."