SOUND-TEANSMITTING APPARATUS OF CAUDATA 369 



a compound fenestral plate which is quite in contrast to the two 

 distinct plates of species composing legion I, where the columella 

 invariably fuses with the ear capsule when its function is reduced. 

 This compound relation of elements represents one which is ob- 

 viously a derivative from the more primitive estate of two dis- 

 tinct and simple elements and one which is reminiscent of a 

 pronounced terrestrial life far back in phylogeny. 



That the Necturidae are neotitic forms, and that they rank 

 with others of the urodele order, has been pointed out by Kings- 

 bury ('09), Norris ('11), Bruner ('14), and others. The morphol- 

 ogy of the sound-transmitting apparatus harmonizes with such a 

 view. This family is adjudged the most primitive of the legion 

 since the fenestral plate is an exact intermediate between others 

 of its group and those composing the amblystomid legion. The 

 columella, during development, spreads out over the surface of 

 the fenestral membrane so as to fill considerably less than half 

 of the window, and fuses with opercular tissue formed within the 

 fenestral membrane itself. This mode of formation reflects a 

 former terrestrial existence for the Necturidae and may be ex- 

 plained by a brief reference to the mode of development of fen- 

 estral elements in Amblystoma and Triton. In the former the 

 'cutting out' process in the production of the operculum is a 

 necessity resulting from the complete filling of the primary fen- 

 estra by the columella, which, in this form, comes into full func- 

 tion and proportions. In Triton the columella is so small be- 

 cause of its functionless state and it fuses so early with the lips 

 of the fenestra that it forms merely a rim of cartilage, thus leav- 

 ing a great portion of the primary fenestra free for the later in- 

 vasion of cartilage, or for its formation within the free membrane. 

 Consequently, in Triton, the operculum is produced, in part, by 

 the cutting-out process, and, in part, by the growth of .cartilage 

 from the edges of the window into the fenestral membrane. 

 The ultimate effect of this trend of modification, then, is the 

 increase of free space in the primary fenestra, within which the 

 opercular element may develop, with no necessity of 'cutting 

 out' from the walls of the ear capsule. Thus one may account 

 for the mode of development and morphology of the fenestral 



