No. 646] THE PHYLOGENY OF THE CAUDATA 421 



form what Reed (1920) calls Legion II, as distinct from 

 the forms which show conditions I-V (exc. Batracho- 

 seps), which Reed calls Legion L 



But the sound-transmitting apparatus of Necturus 

 agrees with that of Amphiuma and the Plethodontidce 

 only in having the columella and operculum fused. 

 There is no reason to suppose that such a fusion may 

 not have occurred twice, especially as the details of the 

 fusion in Necturus differ somewhat from the manner in 

 which the fusion occurs in Amphiuma and the Pletho- 

 dontidce. In Necturus the columella forms a goodly part 

 of the plate-like portion of the apparatus. In the forms 

 of condition VII, the plate-like portion is almost entirely 

 composed of the operculum, and the columella is repre- 

 sented by the stylus. In this case the evidence of the 

 ear bones is non-committal. Considered apart from all 

 other features of the anatomy condition VII might 

 equally well be derived from condition VI or both inde- 

 pendently from condition I. But, as we shall see, evi- 

 dence from other features of the anatomy precludes our 

 regarding Necturus as intervening between the Pletho- 

 dontidm and the other Mutabilian forms. 



It is extremely interesting to note that Reed has found 

 almost exactly the same state of affairs in Amphiuma and 

 in the PlethodontidcB. The exact relationships of Am- 

 phiuma have long been in dispute, and while I prefer to 

 be conservative about the position of the animal, I 

 think it extremely likely that further evidence will show 

 that it is closer to the PlethodontidcB than it was placed in 

 the older classifications. 



Any classification should be based upon all available 

 characters, so that possible parallelisms will not lead to 

 wrong conclusions. In the present instance we are deal- 

 ing with a stock neither absolutely terrestrial nor abso- 

 lutely aquatic. From this stock there have been several 

 branches which have become more aquatic and several 

 which have become more terrestrial. Excellent examples 

 of this are the numerous incursions into a mountain 



