604: B. r. Kingsbury and H. D. Keed. 



imagination could an extra-otic origin be ascribed to the element 

 filling the fenestra vestibuli in this group, was made in the light of 

 the condition existing in Triton and the fragmentary developmental 

 evidence already at hand, and without knowledge of the existence of 

 two structures in urodeles. It applies, therefore, with full force to 

 the development of the operculum. The columella, however, develops 

 in quite a different manner, and here the evidence of an extra-otic 

 origin is much stronger. Killian ('90) first described this structure 

 as developing outside the ear capsule in Ambystoma, and Miss Piatt 

 ('97) in ISTecturus advanced the same view. Kingsbury subsequently 

 examined the condition in larval and embryo Necturi and came to the 

 same conclusion. In this paper we have shown evidence of an 

 entirely similar mode of origin of the columella, outside the f enestral 

 membrane, in Cryptobranchus, Spelerpes, and Plethedon, and con- 

 firmed Killian's observations on Ambystoma. Supplementary evidence 

 of an extra-otic origin for the columella is to be found in the fact that 

 from the first, before chondrification has begun, the columella is 

 connected by a dense grouping of cells with the squamosal cells 

 around the outer side of the vena petroso-lateralis. 



With the growth of the fenestral plate of the columella it becomes 

 associated or fused with the cephalic edge of the fenestra. This is 

 not, however, a primary connection but a secondary one. Hence the 

 statement that has been made (Winslow, Stohr) that the columella 

 grows out of the cephalic edge of the window is not correct. In the 

 descriptive portion of this paper, the difficulty in determining just 

 what occurs in the chondrification of the plate of the columella has 

 been pointed out. Even though the columella grew through the 

 incorporation of otic tissue, its origin from without the otic capsule 

 would not be invalidated, which is supported by its relation before 

 chondrification and its early and intimate connection with the sub- 

 squamosal cells. 



The tendency of the columella to become fused with the cephalic 

 cartilaginous margin of the fenestra is in some forms carried to an 

 extreme, and results in a more or less complete incorporation of the 

 structure into the ear capsule by extensive fusion with it. In the 

 Ambystomidse its boundary is still distinguishable by the charac- 



