The _piscina_ is a hollowed out niche with drain to carry away the water used in the ablutions during mass. After the Thirteenth Century there is scarcely an altar in England without one. Sometimes the _piscina_ is in the form of a double niche. Beneath the cathedral there is often a crypt--in reality a second church, often of great size. “We may be tempted to ask, what is the purpose of a crypt? Some have said that it was merely meant to give dignity to the church, or to avoid the damp. It appears, however, to be a custom taken from the very early Christian churches at Rome, which were in many cases built over the tomb of a martyr, and had therefore a lower and an upper church. Indeed if we imagine the central portion of the choir steps removed so that the nave floor might extend without interruption to the crypt, and a clear view of the crypt be open to the nave, we should have an arrangement precisely similar to that of several Italian churches, notably that of San Zenone, at Verona.”--(F. and R.) As a rule, the monastic buildings, refectory, dormitory, infirmary, etc., were built on the south side, and here were also the cloisters, those pleasant walks and seats for exercise and recreation surrounding a peaceful quadrangle. The slype, or passage on the east side, led to the monks’ cemetery. In the chapter-house the monks transacted their business. The chapter-house, often one of the richest and most beautiful portions of the cathedral, may be of any form. Those of Canterbury, Exeter, Chester and Gloucester are oblong; those of Salisbury, Wells, Lincoln, York and Westminster are octagonal; and that of Worcester is circular. At Salisbury, Wells, Lincoln and Worcester a single massive shaft supports the vault. In examining a cathedral we must remember that many changes have taken place since the first stone was laid. If the monks were fortunate enough to have a full treasury, they kept up with the architectural styles. They would pull down the old nave, or choir, or transepts, and erect new buildings, lower the pitch of the roof, add a new porch or door, or insert new windows in the ancient walls. Fires were frequent and lightning and winds often played havoc with towers and spires. Such manifestations of the displeasure of the elements or saints necessitated rebuilding; and, as a rule, this rebuilding was undertaken in the latest fashion. Therefore, we find in most cathedrals specimens of many styles of architecture.