The Columella Auris in Amphibia. 551 



became necessary to keep in mind the development of each element 

 in its relation to the ear capsule. In the present paper a detailed 

 presentation of the developmental changes, even as far as they have 

 been worked out, is not included. 



In addition to the forms briefly described in the first publication 

 made by us, there have been examined by means of serial sections 

 through the head, 14 species representing 1 family and 12 genera. 

 The total number comprises 8 families, 21 genera, and 23 species, 

 in the case of all save 9 of which the structure and moi-phology in 

 both larvse and adults were investigated. Bearing in mind that the 

 total number of the families and genera of tailed amphibia is 8 and 

 45 respectively, it may be seen that a comprehensive and at the 

 same time detailed view has been gained of the relations of the 

 urodele "sound-transmitting" apparatus. 



Without entering upon a full discussion of the bearing of our 

 investigation, which is reserved for the last portion of this paper, 

 the more important results may be stated briefly at this point. 



1. In the tailed Amphibia, there may be developed two separate 

 fenestral elements fitting into the fenestra vestibidL These have 

 been termed by us ColmneUa and Operculum respectively. 



2. The Columella typically possesses a Stilus which is connected 

 primarily with the ventral (or ventro-caudal) edge of the squam- 

 osum. The Stilus columellw may secondarily become joined to the 

 palatoquadrate. 



3. In development its proton appears outside the otic capsule as a 

 group of cells continuous with the cells between the otic process of 

 the palatoquadrate, squamosum and ear capsule. 



4. The facial nerve in the forms examined is entirely below (and 

 in front of) the columella save in jSTecturus, Proteus and Typli- 

 lomolge, in which the Banwis jugular Is VII passes above the 

 squamoso-columellar connection. 



5. The Operculum, is developed out of the otic capsule. Its posi- 

 tion relative to the columella is caudal and medial. It possesses 

 no skeletal connections but gives attachment to the M. opercularis. 



6. In one group of forms, the columella only is present. In the 

 Ambystomidse the columella is present during the larval period but 



