On the Perilymphatic Spaces of the Amphibian Ear. 251 



be conceived. We have an actual example of a similar adaptation, in 

 the formation of the fibrous band connecting saccus perilymphaticus 

 and lung in Pelobates and E. fusca. The band is simply a modification 

 of elements that already had similar connections, for another purpose, 

 before the recessus partis basilaris passed out of the capsule to form 

 the saccus. I should explain in the same way the association of 

 foreign elements with the membrane of the fenestra vestibuli. In the 

 latter case however, we have not a transitory larval connection, but 

 one which has come to persist as a functional arrangement through- 

 out life. The relations of the operculum to the wall of the capsule 

 and other neighbouring parts, receive their simplest explanation by the 

 aid of the theory that it has been derived from a skeletal element 

 which has been gradually obtaining a greater degree of independence 

 and efficiency as a structure connected with the transmission of vibra- 

 tions to the perilymph. It is even possible that the presence of this 

 foreign element at the point at which the fenestra vestibuli was for- 

 med was prejudicial to the functional value of the membrane, and 

 that progress was in the first case in the direction of a modification 

 which would obviate this disadvantage. This can only be a matter of 

 conjecture, but the appearances in Amphibia certainly suggest that the 

 operculum is not a structure which was from the first a part of the 

 auditory capsule, but rather a foreign skeletal structure which required 

 considerable adaptation to fit it for its function as part of the accessory 

 auditory apparatus.^) 



I have now only to discuss the significance of the association 

 of the perilymphatic spaces with the pars inferior of the labyrinth. 

 I have already pointed out the interest attaching to the fact that 

 the ampullae and maculae of the pars superior have no direct rela- 

 tionship with the perilymphatic system. It can scarcely be a coin- 

 cidence that the pars inferior acquires such a preponderating rôle in 

 the ascending series of the Vertebrata. This is particularly noteworthy 

 in the case of the pars basilaris. In the Urodela the latter structure 



^) A full discussion of the views that have been held as to the origin of the 

 operculum, will be found in the above-quoted paper by Gaupp [11], in which also 

 references to the extensive literature of the subject are given. 



