SOUND-TRANSMITTING APPARATUS OF CAUDATA 343 



years as compared with a few weeks in Amblystoma. During 

 this period they inhabit cool streams, with more or less current, 

 rather than stagnant pools, and are more buoyed up by the 

 water. During late larval life the relation of stylus and cleft 

 is gradually lost, so that at transformation all traces of former 

 connections have disappeared. 



Spelerpes ruber. This species has not been studied with the 

 same detail as S. bislineatus. Larvae from 41 mm. to adults 

 indicate that the relations and morphology of the fenestral ele- 

 ments are identical, except for certain specific variations. In 

 this species the stylus is placed farther dorsad and not quite so 

 firmly joined to the plate, a condition which foreshadows the 

 relation of parts in Gyrinophilus to be discussed next. 



Gyrinophilus porphyriticus. Both the fenestral plate and the 

 fenestra itself in Gyrinophilus are nearly circular, in decided 

 contrast to the elongate structures of Spelerpes. The pletho- 

 dontid mode of ossification is followed. Although larval stages 

 were considered, an examination of older larvae and adults alone 

 is conclusive in the light of the development of these parts in 

 S. bislineatus. There is no pronounced perilymphatic promi- 

 nence as such. The whole fenestral plate represents an out- 

 pocketing away from the fenestral lips which, on the dorsal side, 

 form a conspicuous ledge. The M. opercularis is attached at 

 the middle of the plate, from which there is a conical projection 

 into the muscle (fig. 32) . The cephalic portion of the fenestra is 

 not completely filled, a similarity of detail which this genus 

 bears to Spelerpes. The space between the dorsal edge of the 

 plate and the lips of the fenestra is filled to a certain extent by 

 the dorsal growth of the plate itself, but to a greater extent by 

 the development of the above-mentioned ledge. The downward 

 and backward growth of the squamosal conceals some of the 

 space which persists in this region. 



The relation of the stylus to the plate is a much less close 

 one than in any of the Spelerpes group. In the adult it is a rod 

 lying against the plate, and sections show that, although it 

 touches the plate, there is no fusion until the very tip end of the 

 stylus is reached. Figures 32 and 10 illustrate this point. 



