294 THE SALAMANDER 



physiological experiments which have been carried out with these 



substances. They are fully described in the papers mentioned. 



THE SENSE ORGANS 

 I. THE EAR. 



1. General. 



The auditory apparatus of Urodeles consists, as in all higher verte- 

 brates, of a membranous labyrinth of ectodermal origin for the com- 

 bined functions of balancing the body and the perception of sounds, 

 together with certain skeletal elements modified for the purpose 

 of conveying the auditory stimuli from the external medium 

 to the labyrinth. These two distinct portions have each been the 

 subject of separate investigations by the various workers dealing 

 with the organ of hearing, and accordingly they will also be dealt 

 with separately here. 



2. Skeletal Structures. 



The skeletal portion is the more highly specialized and is very 

 characteristic of the group. 



The earlier authors dealing with the ear of the Salamander, as well 

 as those investigating the structure of the skull in general, recognized 

 only one skeletal element within the fenestra vestibuli (ovalis), namely 

 the operculum. The first investigator to recognize the homologies 

 of all the skeletal parts concerned and to give an adequate account 

 of their relations was Gaupp (1898), but their full significance and 

 mode of operation were not completely understood until the investi- 

 gations of Kingsbury and Reed (1902—20). 



It is perhaps almost unnecessary to point out that the familiar 

 tympanum and tympanic cavity of the Frog are wanting in Sala- 

 mandra, or for that matter in all Urodeles. Nevertheless a columella 

 is -present^ but it remains quite vestigial and does not reach the outer 

 surface, and is a.ppa.rently fuficlionless in terrestrial adults. There is a 

 considerable amount of variation among the several families of Uro- 

 deles, and these differences have been used for classificatory purposes 

 by Reed (1909 and 1920), although Dunn (1923) questions their 

 value in this respect. It is unnecessary to go into the question in 

 detail here, but the reader may refer, either to the original papers 

 quoted, or to the summary given by Goodrich (1930, p. 480). 



In the Salamander there are two structures filling the fenestra 

 vestibuli (ovalis) of the auditory capsule — (i) the columella^ which is 

 extra-otic in origin, and (ii) the operculum^ a cartilaginous plate cut 



