The chamber within is capacious and is ordinarily of conical form, tapering slightly from a low domed roof downward to a bowllike bottom. There may be a slight bulging of the walls below a narrowed median portion. The depth may vary from 10 to 24 inches (extreme figures of 6 and 26 have been recorded). The average of 15 measurements is 19 inches. The entrance hole leads to the upper widest portion, and there the chamber is 7 or 8 inches across. The distance from the outer surface of the hole of the tree to the remote wall of the chamber is about 11 inches. The entrance passageway about 2 inches inward is ridged across, and from this median ridge the floor of the passageway slopes downward, both inwardly and outwardly, and this outward slope forms the bevel already mentioned. The bowl at the bottom is 6 or 6½ inches across. In a specimen before me as I write, the wall of the chamber below the entrance hole is 4 inches thick. The ridge across the floor of the entrance passageway is rounded. Its crest is 2¼ inches inward from the outer surface of the tree trunk, and the vertical depth of the outward bevel is 2 inches. All the surfaces of the cavity are neatly and uniformly chiseled. Along the sides of the entrance passageway extend in parallel curves the tool marks of the bird’s beak. No nesting materials are brought in. A feather or two will be the only trace of occupancy remaining after the young are flown. In some though not in all cases it is possible for a man to thrust in his arm and reach the bottom of the chamber. As a general rule, certainly, a new cavity is drilled for every brood. Such exceptions as have been recorded have explanation in human interference. Samuel Scoville, Jr. (1920), quotes Richard C. Harlow to the effect that but once in his experience had a second use of a nesting cavity occurred. Afterward Mr. Harlow said to me in conversation that even in that instance the cavity had been deepened before it was used for a second time. The only other instance that has come to my attention is one recorded by Morrell (1901) in which a single cavity was used three times--in 1895, in 1897, and in 1898. In preparation for the third nesting the cavity had been deepened by three inches. This nesting was in “a small patch of good sized trees * * * separated [from] the main growth by cutting,” and it may be supposed that the woodpeckers had been unduly limited in the choice of nesting sites. In both cases the birds were subject to the disturbance of persistent egg-collecting. It stands to reason that, in avoidance of parasites, the practice should have evolved of drilling a fresh cavity for each brood.