. Journal of morphology . apparently is joinedto the ceratohyal by a less marked cord of cells. Figs. 8 and 9from two sections 25 microns apart may serve to illustrate the extra-otic position of the columella. Comparison with the figures of likestages of Ambystoma and Cryptobranchus is suggested. In Spei-lerpes larA^se 23 mm. long the lower end of this cord of cellshas become intimately associated with the fenestral membrane atthe cephalo-ventral margin of the fenestra. At this point the fenes- The Columella Auris in Amphibia. 581 tral plate remains permanently fused with the ear capsule. Chon
. Journal of morphology . apparently is joinedto the ceratohyal by a less marked cord of cells. Figs. 8 and 9from two sections 25 microns apart may serve to illustrate the extra-otic position of the columella. Comparison with the figures of likestages of Ambystoma and Cryptobranchus is suggested. In Spei-lerpes larA^se 23 mm. long the lower end of this cord of cellshas become intimately associated with the fenestral membrane atthe cephalo-ventral margin of the fenestra. At this point the fenes- The Columella Auris in Amphibia. 581 tral plate remains permanently fused with the ear capsule. Chon-drification has oocurred, forming a stilus and a small fenestral plate(Figs. 8 and 10). From the place of its attachment the fenestral plate graduallyextends backwards, growth being the result of the deposition of carti-lage in the free margins of the plate, particularly the caudal. Thussuccessive rings are added until the plate fills the opening in the earcapsule. In the caudal portion of the fenestra vestibuli the mem-. FiG. 9. Spelerpes ruber, larva 71 mm. long. , fenestral plate; ,recessus perilymphaticus. brane forms an outpocketiug or prominence (Fig. 12) long beforeit is invaded by cartilage, but before transformation the extensionof the prominence behind the lips of the fenestra is slight if presentat all. The prominence forms the outer walls of a recessus whichhas the same relations as that of the adult. Until transformationthere is no indication of the M. opercularis, it apparently having nofunction until adult life is assumed. The conditions in the adultPlethodontidse are well illustrated by the photographs of Gyrino-philus in Figs. 45, 46, 47 (PI. VI). 582 B. F. Kingsbury and H. D. Reed. It appears that the definitive plate of the adult is the result of adirect and continuous growth of cartilage in the membrane whichcovers the foramen vestibuli. At no time during development arethere found separate centers of chondrification in either stilus orfenestral pla
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