The Columella Auris in Amphibia. 569 



embryos studied. His theoretical conclusions drawn from the devel- 

 opment of the operculum in Salamandra will be referred to in the 

 second part of the paper. 



Tritojst and Diemictylus. 



In Cope's family of the Pleurodelidse, the condition of reduction 

 and incorporation, — if we may so state it, — is carried farther than 

 in the form just described, — Salamandra. The connection with 

 the squamosum and palatoquadratum is absent, and the fenestral 

 plate forms the portion of the ear capsule bounding the cephalic 

 part of the fenestra vestibuli above and in front. In the adult, 

 the identity is entirely lost and it would be impossible to recognize 

 the true morphological relations were it not for the condition in the 

 larva. In fact, at the time of our first contribution, the existence 

 of the columella in Diemictylus was not recognized even though 

 larvae had been examined. At that time we expressed confidence 

 in its presence at some stage in the development of the larva, but 

 thought that it was absorbed or became incorporated, — possibly with 

 the operculum. It was, indeed, subsequently found to be present 

 and incorporated not with the operculum, but with the edge of the 

 fenestra. It was in the light of the conditions in Salamandra that 

 the relations in Diemictylus became clear. The existence of the 

 columella was first determined in a 19 mm. larva, the subsequent 

 examination of Triton larvae bringing confirmation. In this last 

 form the significance of the morphological relations is more apparent 

 so that it may best be considered first. 



Triton crisiatus. Through the kindness of Professor Robert 

 Wiedersheim, we were enabled to examine a series of specimens of 

 this form, serial sections being prepared of larva? 18, 20, 25, 34, 36, 

 and 37 mm. in length. In the smallest individual at our disposal 

 (18 mm.) both operculum and columella are present, of cartilage, 

 the latter fused more or less completely with the crista semicircularis, 

 hence it has been impossible to determine how early this stnicture 

 appears ; Avhether at any time its proton is as obviously outside the 

 membrana fenestrse as it is in Ambystoma, or whether it undergoes 

 chondrification separate and distinct from the edge of the primary 



