338 H. D. REED 



The further development of the fenestral plate is concerned 

 with its ossification and has little or nothing to do with its mor- 

 phology. As mentioned above, the stylus first chondrifies at 

 those points where it comes into contact with the fenestral 

 plate, and from here cartilage gradually extends cephalad until 

 the long dense cord of the columellar proton is transformed into a 

 cartilaginous rod, except for a short ligament which effects the 

 attachment to the squamosum. Ossification in the stylus begins 

 at its fenestral end and proceeds toward the suspensorial attach- 

 ment, as did the chondrification, forming, at first, a shell of bone 

 about a cartilaginous core which gradually diminishes as the 

 bone increases in thickness. In the oldest adults studied car- 

 tilage still persists at the center. 



Ossification of the fenestral plate begins on the ectal surface 

 at the base of the stylus. From this as a center bony tissue 

 spreads toward the periphery and finally the cartilage is entirely 

 replaced by bone, the formation of which gradually extends 

 from the ectal, through the plate, to the ental surface. In 

 Amblystoma the ectal and ental plates of bone are formed 

 independently. 



From the foregoing paragraphs the morphology of the fenestral 

 elements in Spelerpes bislineatus is evident. A brief summary 

 of the morphology and development of these structures in 

 Amblystoma will serve as a basis of comparison in the two 

 forms. In Amblystoma the columella arises as a dense strand of 

 tissue, extending between the ventral edge of the squamosum 

 and the feneptral opening, opposite which the end of the cord 

 of cells expands as the first step in the formation of a plate-like 

 columella which is later completely to fill the fenestral opening. 

 Throughout the developmental period and late into larval life 

 its position outside the fenestral membrane is evident, as shown 

 in figure 7. In late larval life the cephalic and dorsal margins 

 of the plate become included within the membrane, prepara- 

 tory to fusion with the ear capsule. Whether this fusion is 

 effected by the active growth of the columella or of the lips of 

 the fenestra, has nothing to do with the morphology of the ele- 

 ment. Chondrification begins early, and gradually the plate of 



