The Columella Aiiris in Amphibia. 581 



tral plate remains permanently fused with the ear capsule. Chon- 

 drification has occurred, forming a stilus and a small fenestral plate 

 (Figs. 8 and 10). 



From the place of its attachment the fenestral plate gradually 

 extends backwards, growth being the result of the deposition of carti- 

 lage in the free margins of the plate, particularly the caudal. Thus 

 successive rings are added until the plate fills the opening in the ear 

 capsule. In the caudal portion of the fenestra vestibuli the meni- 



FiG. 9. Spelerpes ruber, larva 71 mm. long. F.p., fenestral plate ; R.p., 

 recessus perilympbaticus. 



brane forms an outpocketing or prominence (Fig. 12) long before 

 it is invaded by cartilage, but before transformation the extension 

 of the prominence behind the lips of the fenestra is slight if present 

 at all. The prominence forms the outer walls of a recessus which 

 has the same relations as that of the adult. Until transformation 

 there is no indication of the M. opercularis, it apparently having no 

 function until adult life is assumed. The conditions in the adult 

 Plethodontidse are well illustrated by the photographs of Gyrino- 

 philus in Figs. 45, 46, 47 (PI. VI). 



