. Journal of morphology . 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 plate-There appears to be a wide divergence between the sound-trans-mitting apparatus in the Plethodontidse and that in seems particularly true of the development, and as a consequenceis also true of the homology of parts. A brief review of the devel-opment of the fenestral elements in the
. Journal of morphology . 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 plate-There appears to be a wide divergence between the sound-trans-mitting apparatus in the Plethodontidse and that in seems particularly true of the development, and as a consequenceis also true of the homology of parts. A brief review of the devel-opment of the fenestral elements in the forms thus far consideredmay, therefore, render the situation easier to grasp. In Ambystomathe ear capsule chondrifies early and the columella fills the fenestravestibuli. At transformation (there being no room for growth) theoperculum is cut out from the cartilage of the ear capsule itself;an adaptation, it might seem, to mechanical needs. In Triton andDiemictylus the columella relatively early fuses completely with the. Fig. 10. Spelerpes bislineatus, larva 43 mm. long. C, arteria carotisinterna; , canalis lateralis; , cavum perilymphaticum; , fenestralplate; L., lagena; M., musculus cephalo-dorso-mandibularis. ear capsule, leaving the foramen free. Here it is found that, whilethere is a slight cutting out of the operculum from the ear capsule,it results largely from a growth of the cartilage cephalad into the fen-estral membrane. The situation in the Plethodontidse differs fromeither of these. The columella, when first coming into intimate rela-tion with the ear-capsule, is small as compared with the size of the for- The Columella Auris in Amphibia. 583 amen which increases in size with the growth of the skull. The earlyossification of the ear capsule renders impossible the formation ofan operculum by either the cutting out process or by forward growthinto the fenestral membrane. A comparison of Figs. 11 and 12 willhelp to make clear that the membrane filling the
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