346 H. D. REED 



ella and operculum, or their corresponding parts, in the whole 

 series of caudate forms reveals a fairly uniform relation of the 

 sound-transmitting organs to parts of the membranous ear. The 

 operculum occupies a position directly opposite the caudal ele- 

 ments of the inner ear. It never extends farther cephalad than 

 the caudal half of the lagena cochleae, thus including the extreme 

 caudal extent of the sacculus only. Cross-sections in some cases 

 do not contain the sacculus at all. The whole plate in Batra- 

 choseps attenuatus is entirely caudad of the sacculus. It appears 

 evident that the columellar element is absent in this form, and 

 that which is present represents the operculum of other forms. 

 The uniform conditions and mode of development of the fenes- 

 tral structures in the Plethodontidae would not suggest a mode 

 of development and morphology different in fundamentals for a 

 particular genus. Taking this view, it appears that the columella 

 (stylus) has failed to develop or at least to reach the definitive 

 state. The slight relations of the stylus and plate in all pletho- 

 dontids are in line with such an explanation. Batrachoseps is a 

 strictly terrestrial species. If, as is the case with others of its 

 family living under similar conditions, the larval state is passed 

 within the egg, there is no need of a columella, and quite natu- 

 rally it should disappear. In the adult a strong cord of tissue 

 extends from the ear capsule between the artery and vein of the 

 region to the squamosum which may represent the vestigial 

 columella. The absence of the isthmus points to cartilage 

 formed within the fenestral membrane as the source of the plate 

 which becomes functional in the adult. 



If these deductions prove true, then Batrachoseps represents 

 the extreme in specialization of sound-transmitting apparatus 

 among the Plethodontidae. 



FAMILY DESMOGNATHIDAE 



Desmognathus fusca, of all the plethodontid types studied, 

 shows most clearly the independent origin and definitive state 

 of the stylus and fenestral plate. In the morphology and rela- 

 tion of parts there is perfect agreement with Spelerpes, and the 

 development is such that no doubt is left with regard to the 



