SOUND-TRANSMITTING APPARATUS OF GAUD ATA 341 



dorsal extension of the cleft is reduced to an open and slight 

 evagination of the oral epithelium toward the margin of the fenes- 

 tra, where it takes up a position between the artery and vein 

 and comes into actual contact with the perichondrium of the 

 developing isthmus fenestralis and the fenestral membrane (figs. 

 8 and 9). At the same time it is connected by a thin sheet of 

 fascia with the columellar proton. In older stages it loses a 

 close connection with the fenestral plate, but retains its rela- 

 tions with the stylus columellae which has become chondrified 

 (fig. 4). 



A comparison of Amblystoma and Spelerpes larvae with re- 

 gard to the relations of the fenestral elements and the hyoman- 

 dibular cleft appears as a favorable argument for the belief that 

 in Spelerpes the persistence and relations of the cleft are closely 

 associated with a function, aside from any morphological sig- 

 nificance which they may have. Without close observation and 

 experimentation it is difficult to form a definite opinion of what 

 that function may be. Judging from the nature of the rela- 

 tions, it might be of use, either as an aid in the apprehension 

 and deglutition of food, or in the detection of disturbances in 

 the water. Comparative evidence favors the latter. In Ambly- 

 stoma larvae no such relations between oral epithelium and 

 fenestral structures exist. Correlated with that condition it is 

 notew^orthy that the columella in amblystomid forms not only 

 arises, but chondrifies, early in development, so that it is able 

 to function as soon as an active free life begins. On the other 

 hand, in Spelerpes the fenestral structures, especially the stylus, 

 are tardy in their development. The larvae are active free- 

 swimming organisms long before a well-defined and functional 

 columella places the inner ear in communication with the sus- 

 pensorium. This, together with the early connection of the cleft- 

 vestige with the end of the growing isthmus and its later relation 

 to the stylus, are significant. Of further interest in this con- 

 nection are the observations of Bruner ('14) which would indi- 

 cate that the water in the mouth forms a means for the trans- 

 mission of disturbances between the environment and the 

 inner ear. The larval period of this species is, at least, two 



JOURNAL OP MORPHOLOGT, VOL. 33, NO. 2 



