SOUND-TRANSMITTING APPARATUS OF CAUDATA 347 



significance of structure. In certain minor details Desmognathus 

 resembles Gyrinophilus more than other Plethodontidae, but in 

 others it reflects conditions found in Plethodon. Concerning 

 Desmognathus, Kingsbury and Reed wrote: ''An examination of 

 3^oung larvae and embryos which would determine the origin or 

 origins of the stylus and fenestral plate has not been undertaken. 

 The mode of insertion of the stylus upon the fenestral plate, 

 . . . . might suggest that the stylus alone developed out- 

 side the otic capsule as the description of Parker would indicate." 

 A study of the development substantiates this statement and 

 proves the correctness of Parker's views. As detailed a study 

 as possible of Desmognathus was undertaken, because, at the 

 time the work was begun, it was believed to represent a distinct 

 family. A careful consideration of the group is justified, since 

 it has strengthened conclusions regarding the relationships of 

 this family, to be mentioned later, and aids in interpreting the 

 general nature of these parts in Spelerpes, where they are found 

 in a more generalized state. 



An examination of the insertion of the stylus upon the plate 

 gives the impression of a knob pressed into plastic material to 

 which it adheres. In medium-sized adults the two structures 

 are easily distinguished in sections, as shown in figure 11. The 

 columella (stylus) arises in the typical way as a cord of cells in- 

 dependent of the ear capsule. It is not yet chondrified in larvae 

 26 mm. long. The cord of cells, however, is very distinct (fig. 

 12) and lies against the fenestral membrane for about 40 m, when 

 it ends abruptly. In this stage the isthmus fenestralis has ex- 

 tended some distance into the membrane, and isolated centers 

 of chondrification, consisting of scattered cells, appear in the 

 middle and caudal parts of the membrane. These cells are 

 formed within the membrane, with no relations to extraotic ele- 

 ments. Figure 13, from a transection 40 ^ caudad of the end of 

 the columellar cord and through the apex of the isthmus, shows 

 the position and relation of the cells just mentioned. Still fur- 

 ther caudad chondrification has begun at several distinct places 

 (fig. 14). The areas of cartilage are not yet associated with 

 others at any level, but show growth in every direction and the 



