The Columella Aiiris in Amphibia. 605 



teristic inner and outer bony plates, and by the stilus. Salamandra 

 lacks the ossification, the incorporation appears more intimate but 

 the stilus is persistent. In Triton and Diemictylus stilus and ossi- 

 fication are both lacking and incorporation into the edge of the 

 fenestra is complete. 



Attending the fusion of the columella, there is the formation of 

 the operculum to inherit its position and function as a fenestral 

 structure. Concerning its origin and development there is not, as in 

 the case of the columella, opportunity for uncertainty. In Ambys- 

 toma, in which it appears late, — at the end of transformation, — it is 

 cut out of the floor of the otic capsule medial to the fenestra. In 

 Diemictylus and Triton, in which it appears early, "cutting out" 

 must play a more secondary part, and marginal growth by chondri- 

 fication of opercular tissue seems more important. It occupies in 

 either event the same position and seems to be a detached portion of 

 the otic capsule, although extensive cartilage formation in it may 

 give it a thickness several times that of tlie otic capsule. It under- 

 goes no ossification, remaining cartilaginous throughout life.^*^ Its 

 characteristic features, negative and positive, are the lack of connec- 

 tion with the skeleton outside the ear capsule, and the attachment of 

 the M. opercularis. 



The fusion of the columella causing a more or less extensive 

 filling in of the cephalic portion of the fenestra vestibuli necessitates 

 the recognition of primary, secondary and definitive fenestrae, of 

 somewhat different boundary and location, as in the Anura (Gaupp, 

 '93). The question of in how far the cephalo-caudal succession of 

 fenestral elements or the (essentially) cephalo-caudal extension of 

 the fenestra itself is an expression of the play of factors of relative 

 growth of parts, — otic capsule, suspensorium, etc., — is simply raised. 

 It is hardly necessary to state that the primary character of the 

 fenestra as an unchondrified portion of the otic capsule, as affirmed 



"It is interesting to find Parker ('S2a) commenting on this condition; on 

 page 199 he says : "One more point of interest is to be noted here : the lowest 

 Perennibranchs have their stapes thoroughly ossified (i. e., the columella) ; 

 the highest Caducibranchs, like the Batrachia, have it (j. e., the operculum) 

 soft ; here in Spelerpes it ossifies early, and becomes a very perfect and 

 elegant shutter to that small oval window." 



