65] THE NA SA L ORG A N IN A MPHIBIA —HIGGINS 65 



Cope (1889) misled by a supposed ethmoid bone in Amphiuma placed 

 the Caecilians with the Urodeles, in which view he was later supported by 

 the Sarasins (1890). Kingsley (1902) definitely determined the position 

 of the Caecilians and maintained Huxley's conclusion that the Gymno- 

 phiona have probably separated from the ancestral Amphibia back in the 

 early Carboniferous period. The nasal capsule of Epicrium is further 

 evidence of the wide divergence of this group from all other Amphibia. 



The Anura are readily separated into two groups, on the basis of the 

 nasal skeletons, and these agree with the extablished classification into the 

 Aglossa and the Phaneroglossa. Cope's subdivision of the latter into 

 Arcifera and Firmisternia is not so readily recognized in the nasal capsules 

 of my material, although there are more resemblances between the cap- 

 sules of Bufo and Hyla, than of either with that of Rana. 



AMPHIBIAN ANCESTRY 



The Amphibians appear, as Stegocephals, in the Carboniferous period, 

 and although from the first they are considerably diversified, there is not 

 known a single trace of any tetrapodous vertebrate in the Devonian with 

 the sole exception of a single footprint from the Pennsylvanian. In the 

 Devonian and somewhat earlier, fishes belonging both to the Dipnoi and to 

 the Crossopterygian ganoids occur, and both of these piscine groups have 

 been invoked by various zoologists as the ancestors of the Amphibia, 

 possibly the tendency of the evidence at present favoring the Crossoptery- 

 gian s. 



All of the amphibians of the Carboniferous, with the possible exception 

 of Pelion, were caudate. Moodie (1916), the latest to study these ancient 

 forms, is inclined to regard Micrerpeton, a small Salamandra-like form, as 

 representing the ancestors of the modern groups, with Necturus as an 

 annectant genus. He bases this conclusion upon the resemblances of the 

 skull, the form of vertebrae and ribs, the peculiarities of the lateral line 

 system, and the presence in both of 'ventral scutellations/ a view which 

 closely resembles the earlier ideas of Cope. 



But it would seem as if Moodie was leaning upon a weak reed in invok- 

 ing ventral scutellations as an argument, no matter what view one may 

 take with regard to the other points of resemblance. It is well known 

 that many of the Stegocephals had ventral scutes, plates or bars upon the 

 ventral surface of the body, but the universal view is, that these structures 

 were purely dermal, belonging like scales of fishes to the skin. Moodie 

 cites Wilder as stating that Necturus had small cartilages in the ventral 

 region, and apparently he regards these as the homologue of the ventral 

 armor of Stegocephals. But there are very important differences between 

 the two. 



