Thus far the discussion of chevets has been distinctly from a structural point of view, but there remain certain other differences between these vaults which are worthy of remark. In the first place, there is the matter of the number of cells comprised in the chevet. The standard during the best Gothic period was seven, though five was a frequent number and quite often nine are found (Plate II-s), as for example, in the apse of San Francesco at Bologna, Saint Martin at Ypres, Belgium, and that of Béziers (Hérault), cathedral (1215-1300).[390] In the smaller churches and in the radiating chapels there are frequently three. Moreover, when the apse has a central pier,[391] there are an even number of bays and thus four and six-celled chevets are employed. That in Saint Pierre at Caen, for example, has four bays all on the curve, and that in Notre Dame at Caudebec-en-Caux (Seine-Inférieure) (fifteenth and sixteenth centuries) (Plate II-t) has only two bays thus placed, a fact which gives an angular character to the apse which is far from pleasing.[392] As for the chevets with six cells, they are of very infrequent occurrence, though one is to be seen in Saint Pierre at Auxerre (Plate II-u). A chevet with the unusual number of eleven cells is to be seen in the church of La Chapelle-sur-Crécy (thirteenth century).[393] In construction, this chevet is similar to one bay of such an eight-part vault as that at Provins, Saint Quiriace[394] with its easternmost cell divided into five parts. THE USE OF A CENTRAL PIER IN THE APSE