The Columella Auris in Amphibia. 571 



Three photographs (PL VII, Figs. 48, 49 and 50) of sections 

 from the 36 mm. larval Triton are submitted in illustration of what 

 has been said above. Fig. 48 is through the ear capsule cephalad 

 of the (secondary) fenestra at a point where the columella is fused 

 with the ventral lip of the (primary) fenestra (cf. Fig. 27, PI. II). 

 It shows the cleft between the dorsal margin and the crista semi- 

 circularis whose existence has been mentioned above. It might also 

 be compared with Figs. 28 and 29, Plate XV, of Gaupp's ('93) 

 monograph upon the Chondrocranium of the Frog. Fig. 49 is five 

 sections (75 microns) farther caudad through the columella and 

 just ahead of the tip of the operculum, while Fig. 50 is still farther 

 back (210 microns) behind the caudal end of the columella and 

 through the operculum. The position of the artery and vein may 

 be noted, in comparison with Figs. 8, 9 and 10 of Stohr ('79). It 

 may be remarked that in the oldest of the larval Tritons examined 

 (37 mm.) the M. opercularis has not yet appeared nor has the oper- 

 culum become completely separated off from the cartilaginous ear 

 capsule. 



By comparing these figures (PI. VII, Figs. 48-50) and the two 

 similar ones of a Diemictylus larva (Text Figs. 4-5) with the sections 

 through the ear capsule of the larval and transforming Ambystoma 

 (PI. Ill, Figs. 31-32-33) the basis of the homologies for Triton 

 becomes evident. In a comparison of Triton and Ambystoma the 

 early appearance of the operculum in Triton is noteworthy. Its 

 proton is already partially outlined at 18 mm. in length, and doubt- 

 less recognizable at a still earlier stage, while in Ambystoma its 

 appearance comes only with the beginning of transformation, and 

 in the larva it is a part of the otic capsule. The columella element, 

 on the contrary, while already evident in the youngest Triton larva, 

 becomes more prominent in the later larval stages ; in Ambystoma it 

 appears very early. The growth of the columellar plate in Triton 

 during the larval period with an increasing distinctness of demarca- 

 tion from the crista semicircularis suggests, it must be admitted, 

 the interpretation of a differentiation out of "fenestral tissue" as 

 the fenestra increases in extent. As has been said, the available 

 material does not permit us to determine the early transformations 



