628 



itself being represented by a portion of the saccular wall. In other 

 fishes (e. g. most "Teleosts") the lagena is a distinct sac-like evagi- 

 nation of the sacculus, and possesses its own macula acustica. This 

 condition is also found in the lower Urodela (e. g. Necturus, Proteus), 

 but in the higher Urodeles (e. g. Salamandra, Triton) the upper part 

 of the wall of the lagena, near the opening into the sacculus, is 

 evaginated to form a very small sac, with a sensory area and with a 

 wall thickened over part of its extent ("Knorpelrahmen") in such a 

 way as to leave a thin membranous area which is in close relation to 

 a perilymphatic space. This is the beginning of the pars basilaris, 

 and, as I have pointed out in a previous paper (6), it is highly prob- 

 able that the close association with the perilymphatic system has been 

 the determining factor in the progressive evolution of this part of the 

 pars inferior. In the Anura the pars basil aris reaches a much higher 

 stage of development, though it is still smaller in size than the lagena. 

 The wall in now more conspicuously adapted to allow of vibration 

 of the thin area, and the papilla is situated near to (but not on) this 

 thin part of the wall. The lagena and the pars basilaris open inde- 

 pendently, though close together, into the posterior portion of the 

 sacculus, and the pars basilaris is situated posteriorly and slightly 

 dorsal to the lagena. 



It is when we come to the transition from the Amphibian to the 

 Reptilian (Sauropsidan) condition that Dr. Alexander disagrees with 

 other observers. The established view, to which I adhere, is that the 

 Reptilian cochlea essentially resembles the Amphibian, and that the lagena 

 and pars basilaris, by partial (almost complete) fusion, have given rise to 

 the single cochlear sac of the Reptilia, which opens by a short tube into 

 the posterior portion of the sacculus. It is well known that the anterior 

 part of this sac possesses an independent functional sensory area, and 

 this is always regarded as the papilla lagenae, and as being homologous 

 with the structure so named in the Amphibia. The posterior portion 

 has its papilla basilaris, which, as I hope to show in a subsequent 

 paper, corresponds to a portion only of the Amphibian papilla basilaris, 

 the greater part of this degenerating 1 ). From the condition found in 



1) In the Reptilia the papilla basilaris is no longer on the thickened 

 part of the wall, but lies on the thin vibratory membrane (basilar mem- 

 brane). It is interesting to note that as soon as a sensory epithelium 

 is developed in such a position, we have evolved a type of sense-organ 

 such as is found nowhere else in the labyrinth. It would seem desirable, 

 in order to emphasize this distinction, that the term "papilla" should 

 be used only for the papilla basilaris of forms above the Amphibia. In 



