582 B. F. Kingsbmy and H. D. Keed. 



It appears that the definitive plate of the adult is the result of a 

 direct and continuous growth of cartilage in the membrane which 

 covers the foramen vestibuli. At no time during development are 

 there found separate centers of chondrification in either stilus or 

 fenestral plate. 



There appears to be a wide divergence between the sound-trans- 

 mitting apparatus in the Plethodontidse and that in Ambystoma. 

 This seems particularly true of the development, and as a consequence 

 is also true of the homology of parts. A brief review of the devel- 

 opment of the fenestral elements in the forms thus far considered 

 may, therefore, render the situation easier to grasp. In Ambystoma 

 the ear capsule chondrifies early and the columella fills the fenestra 

 vestibuli. At transformation (there being no room for growth) the 

 operculum is cut out from the cartilage of the ear capsule itself; 

 an adaptation, it might seem, to mechanical needs. In Triton and 

 Diemictylus the columella relatively early fuses completely with the 



Fig. 10. Spelei'pes bislineatus, larva 43 mm. long. C, arteria carotis 

 interna ; C.I., canalis lateralis ; C.p., cavum perilymphaticum ; P.p., fenestral 

 plate ; L., lagena ; M., musculus cephalo-clorso-mandibiilaris. 



ear capsule, leaving the foramen free. Here it is found that, while 

 there is a slight cutting out of the operculum from the ear capsule, 

 it results largely from a gi-owth of the cartilage cephalad into the fen- 

 estral membrane. The situation in the Plethodontidse differs from 

 either of these. The columella, when first coming into intimate rela- 

 tion with the ear-capsule, is small as compared with the size of the for- 



