40 ILLINOIS BIOLOGICAL MONOGRAPHS [40 



COMPARISON OF THE NASAL CAPSULES IN THE 

 URODELA AND GYMNOPHIONA 



The nasal capsules of several families of Urodeles afford a basis for 

 the division of this order of Amphibia into four groups, founded upon 

 similarity of larval structures and the method of chondrification. In 

 some forms, where larval characters were not at hand, adult characters 

 were employed in the classification; in others the early process of develop- 

 ment was the only criterion available. Of these groups, Spelerpes, 

 Plethodon and Amblystoma form one; Salamandra, Triton and Diemicty- 

 lus another; Amphiuma, although remote from Cryptobranchus in the 

 later stages, is included with it in the third; while Necturus remains alone 

 in the fourth group. 



To recognize in the nasal capsules of the Urodela a complete phylo- 

 genetic development or gradual transition from one animal to another is 

 impossible, for many gaps exist, concerning which evidences of structural 

 relationships are wanting. On the other hand many resemblances in the 

 development of certain structures in the nasal capsule may throw some 

 light upon the inter-relationships of this Amphibian order. 



Of the Urodeles included in this study, it would seem as if the capsule 

 of the American species of Cryptobranchus possesses characters most 

 ancestral and which show relationships to both Urodela and Anura. Re- 

 garding Cryptobranchus, then, as more primitive, Spelerpes, Plethodon 

 and Amblystoma appear in an ascending series from the primitive condi- 

 tion; while Salamandra, Triton and Diemictylus are separated from them, 

 but possibly related to them through some form like Spelerpes. Necturus 

 may be regarded as a neotenic condition of Spelerpes, while Amphiuma is 

 possibly reduced from the more primitive Cryptobranchus. 



The two weeks larva of Cryptobranchus has a well-developed trabecular 

 crest which is not present in corresponding stages of Spelerpes or Ambly- 

 stoma; in the latter of which the development of the crest is apparently 

 correlated with the chondrification of the ethmoidal column. Thus it 

 would appear that in Cryptobranchus the dorsal crest is developed before 

 the column, while in Amblystoma the reverse is true. In this respect, 

 Spelerpes is intermediate between Cryptobranchus and Amblystoma, 

 although more like the former; for in the only available stage of the older 

 larva of Spelerpes, the crista is well developed, while the columna eth- 

 moidalis is but partly chondrified. My material does not show the origin 



