In late January 1875, "The Times" ran advertisements for the Royalty Theatre: "In preparation, a new comic opera composed expressly for this theatre by Mr. Arthur Sullivan, in which Madame Dolaro and Nelly Bromley will appear." Reginald Allen and other writers took this as an advertisement for "Trial by Jury". However, as George McElroy noted, the advertisement does not mention a librettist, a peculiar omission if it was to have been W. S. Gilbert, since Gilbert was, at that point, better known to London theatregoers than Sullivan. Moreover, "Trial" has no place for two principal ladies, but "The Zoo" does. McElroy demonstrated that the January advertisement definitely was not for "Trial", when he discovered a further advertisement in "The Era" of 14 March 1875, which noted that "In consequence of the continued success of "La Périchole", the production of Mr. Sullivan's two-act opera is postponed." That two-act work must have been something entirely different from "Trial by Jury", which is in one act, and which opened just eleven days later.