Question: Found the following article online, use it to answer the question: What is the name of the instrument for which Saint-Saëns's pupil left no legacy of works?  Nichols comments that, although as a famous pianist Saint-Saëns wrote for the piano throughout his life, "this part of his oeuvre has made curiously little mark". Nichols excepts the Étude en forme de valse (1912), which he observes still attracts pianists eager to display their left-hand technique. Although Saint-Saëns was dubbed "the French Beethoven", and his Variations on a Theme of Beethoven in E♭ (1874) is his most extended work for unaccompanied piano, he did not emulate his predecessor in composing piano sonatas. He is not known even to have contemplated writing one. There are sets of bagatelles (1855), études (two sets – 1899 and 1912) and fugues (1920), but in general Saint-Saëns's works for the piano are single short pieces. In addition to established forms such as the song without words (1871) and the mazurka (1862, 1871 and 1882) popularised by Mendelssohn and Chopin, respectively, he wrote descriptive pieces such as "Souvenir d'Italie" (1887), "Les cloches du soir" ("Evening bells", 1889) and "Souvenir d'Ismaïlia" (1895). Unlike his pupil, Fauré, whose long career as a reluctant organist left no legacy of works for the instrument, Saint-Saëns published a modest number of pieces for organ solo. Some of them were written for use in church services – "Offertoire" (1853), "Bénédiction nuptiale" (1859), "Communion" (1859) and others. After he left the Madeleine in 1877 Saint-Saëns wrote ten more pieces for organ, mostly for concert use, including two sets of preludes and fugues (1894 and 1898). Some of the earlier works were written to be played on either the harmonium or the organ, and a few were primarily intended for the former.
Answer:
organ