The Columella Auris in Amphibia. 



575 



2-3), the operculum is plate-like, of cartilage, having the same 

 relations to the fenestral margin as in Triton. It is somewhat more 

 massive ; the fenestral margin is cartilaginous only in front and 

 above where the cartilage extends back to the caudal end of the 

 fenestra. Below, cartilage extends back only as far as the anterior 

 "tip of the operculum. A well developed M. opercularis is present. 

 During the larval stage the morphological relations are essentially 

 those of Triton lan'se, the vestigial plate being somewhat more 

 closely joined to the crista semicircularis (Fig. 4, Cr. s.), but its 



Fig. 2. Fig. 3. 



Fig. 2. Diemictylus viridesceus, laud form. G.L, canalis lateralis ; C.p., 

 cavum perilymphaticum ; D.p., ductus perilynipliaticus ; H., ceratoliyale ; 

 Op., operculum ; >S'(/., os squamosum. 



Fig. 3. Diemictylus viridesceus, laud form. C.I., caualis lateralis ; C.p., 

 cavum perilymphaticum; D.p., ductus perilymphaticus ; H., ceratohyale; 

 Op., operculum ; N.p., recessus perilymphaticus ; Sq., os squamosum. 



ventral edge more evidently outside the membrana fenestrae. At 

 15 mm. in length, neither columella nor operculum have appeared. 

 In a 17 mm. specimen, the columella is developing upon the fenes- 

 tral membrane in continuity with the fenestral margin above and in 

 front. The operculum is forming on the medial edge of the fenestra 

 in continuity with the cartilage of the capsule. Aside from growth 

 and a more marked differentiation of the operculum, there has been 

 but slight change in a larva 19 mm. long. At 37 mm. the operculum 

 and also the columellar plate are well developed. The relations 



