. Journal of morphology . respects there is a striking similaritybetween the caudal portion of the fenestral plate in the Plethodon-tidse and the operculum of other forms. Further than the similari-ties mentioned in the preceding paragraph there is, in the adult, noevidence as to the constitution of the fenestral plate in the Pletho-dontidss. In the light of development, however, the condition is 580 B. F. Kingsbuiy and H. D. Keed. somewliat better understood. Eleven larvse of Spelerpes bislineatusranging in length from 15 to 55 mm. were studied by means ofserial sections. Just when the colume
. Journal of morphology . respects there is a striking similaritybetween the caudal portion of the fenestral plate in the Plethodon-tidse and the operculum of other forms. Further than the similari-ties mentioned in the preceding paragraph there is, in the adult, noevidence as to the constitution of the fenestral plate in the Pletho-dontidss. In the light of development, however, the condition is 580 B. F. Kingsbuiy and H. D. Keed. somewliat better understood. Eleven larvse of Spelerpes bislineatusranging in length from 15 to 55 mm. were studied by means ofserial sections. Just when the columella makes its appearance wecan not say, but in larvse 15 and 17 mm. long there is present a deli-cate cord of cells outside the ear capsule extending from the underside of the squamosum towards the fenestral membrane to whichit is not closely related at this stage. In a larval Plethodon cinereus(Figs. 6 and Y) of a similar stage of development this cord iscomposed of a greater number of cells and is consequently more com-. Col. 6. Fig. 8. Spelerpes bislineatus, larva 23 mm. loug. C, arteria cardtisinterna ; , canalis lateralis ; Col., columella ; Cp., cavum perilymphaticum ;, vena petroso-lateralis. pact and larger. Here also, as in Spelerpes, this group of cells isnot closely connected with the fenestral membrane. It extends for-ward to the under side of the squamosum and 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
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