The extant compositions of this master are seventeen masses, seven motets, nineteen chansons, and a number of canons. One mass is in the possession of the papal chapel, and five of the chansons were published by Petrucci early in the sixteenth century, not long after Okeghem’s death. The _Missa cujusvis toni_ was used for many years in the cathedral at Munich, where the MS., with corrections made by the singers themselves, still exists. Another mass, _Deo gratia_, has become one of the curiosities of musical history, from the fact that it is written for thirty-six parts, with a nine-fold canon. It may be said at once that Okeghem’s celebrity, and his important place in the history of polyphony, rest upon two things: his remarkable influence as a teacher, and the fact that under him and his pupils the canonic style, in extremely ingenious combinations, reached the apogee of its development. Preceding composers had studied and written much about the proper manner of treating two or more melodies in combination, about intervals, progressions, dissonances, mensural problems, and the art of imitation, diminution, inversion, and the like. Some of them had expended their genius in systematizing and classifying the complex rules for contrapuntal writing, and they delighted in setting themselves difficult tasks to be performed within these rigid rules. This was all very well; it resulted in the establishment of a perfected technique and a body of knowledge, the value of which was recognized by every musician with scholarly aims. Okeghem appeared on the scene at a time when the struggle with technical difficulties seemed to be an end in itself, and his genius--of the mathematical sort--enabled him to master and play with them. It is a mistake to suppose that he devoted himself wholly, or even largely, to the composition of more 'riddle canons,’ as they are called; but it is probably a fact that he is most frequently remembered and characterized by them. [Illustration: RIDDLE CANON by PIERRE DE LA RUE.]