252 H- S. Harrison, 



is of small extent and probably represents an outgrowth of the wall of 

 the lagena. It has however a tjnnpanal area, and does not differ in 

 any essential feature from the pars basilaris of the Anura. In the 

 latter group it is much larger in size, and has acquired greater inde- 

 pendence. Its tympanal area is stretched across what must be an 

 extremely rigid frame and there can be no doubt as to the functional 

 efficiency of the arrangement. Gegenbaur^), in speaking of the evolution 

 of the cochlea, says: "Jene Ausbildung eines Labyrinthteils gründet sich 

 wohl auf den qualitativ höheren Wert, tvelcher schon mit dem frühesten 

 Zustand des Organs darin sich ausspricht, dass eine die Nerv- 

 endigungen tragende Memhran an der SJceletivand des Labyrinths 

 zur Befestigung tuie in einem Rahmen gelangte und damit den Schall- 

 wellen percipierenden Apparat zu einer viel feineren Einrichtung 

 Jcommen Hess." From the context this can only refer to the pars basi- 

 laris of the Anura. As I have before pointed out, the "Knorpelrahmen" 

 is not part of the "Skeletwand" of the capsule. Neither is the macula 

 of the pars basilaris situated on the tympanal area, as Gegenbaur implies. 

 Therefore, although I attach great importance to the arrangements for 

 the transmission of vibrations to the pars basilaris, my opinion 

 is based in part on different grounds from those brought forward by 

 Gegenbaur. I believe that the early association with a perilymphatic 

 space, and the development of a rigid skeletal wall serving as a frame 

 to support a thin membrane which separates endolymph and perilymph, 

 are factors that have played no small part in the progressive evolution 

 of the cochlea. These conditions are already found in the Urodela. 

 In the Anura, in addition to an undoubted advance in the structure of 

 the pars basilaris itself, the applied perilymphatic space has obtained 

 an outlet from the auditory capsule, thereby entering on direct re- 

 lationships with the exterior. 



The connection between the lung and the saccus perilymphaticus 

 in the two cases I have described, is evidence of the importance of 

 this part of the perilymphatic system at a certain (larval) period. We 

 may even conjecture that it is due to the favourable start obtained 



') Vergleichende Anatomie der Wirbeltiere. 1898. Bd. I. S. 892. 



