362 H. D. REED 



restrial period of existence, as pointed out by Gsge ('91). The 

 other extreme (the less modified) is found in the Amblystomidae 

 and Salamandra, the latter in many respects exhibiting features 

 which foreshadow the Triton state. The columella in this le- 

 gion, although fusing with the ear capsule in varied degrees, 

 shows, nevertheless, its characteristic spreading over the fenes- 

 tral membrane during development. The plate thus formed does 

 not fuse with the operculum or contribute to it in any way what- 

 soever. In no other caudates does this state obtain. 



Although the columellar element in Siren is unknown, the mor- 

 phology of the operculum is sufficient for the inclusion of this 

 family among those of legion I. There are, however, certain 

 features of habit and morphology which seem to be at variance. 

 Thus it appears that the type of sound-transmitting apparatus 

 found only in terrestrial urodeles is here present and well defined 

 in an aquatic species. It seems desirable, therefore, to intro- 

 duce whatever there may be of evidence upon this point gained 

 from other studies upon this species. Cope ('85) was the first to 

 point out that the present aquatic abode of Siren is secondary, 

 following a period of terrestrial existence. His conclusion was 

 based upon a tendency of the gills to disappear and become func- 

 tionless in specimens of a certain age, reaching full development 

 again only in large adult specimens. He writes: ''The only ex- 

 planation appears to me to be that the present sirens are the de- 

 scendants of a terrestrial type of Batrachia, which passed through 

 a metamorphosis like other members of their class, but that 

 more recently they have adopted a permanently aquatic life, and 

 have resumed their branchiae by reversion." In a later publica- 

 tion, Cope ('88) expressed the belief that he had found confirma- 

 tory evidence in the support of this view in the structure of the 

 ossicula auditus. The morphology of the sound-transmitting 

 apparatus as deciphered in the present study supports Cope's 

 belief for an operculum, of whatever mode of formation, in com- 

 munication with the shoulder-girdle, is associated only with a 

 terrestrial existence, and, if its function has been correctly inter- 

 preted, is useful in such an environment only. The period of 

 terrestrial existence of the antecedents of the present Siren must 



