340 H. D. KEED 



While the development of the sound-transmitting apparatus in 

 Spelerpes bislineatus shows many differences of detail from that 

 of Amblystoma, it conforms, nevertheless, to the statement 

 made by Kingsbury and Reed regarding the nature of this 

 apparatus in urodeles generally. That is, there are two distinct 

 elements present. The growth of the fenestral plate into the 

 membrane from the lips, or its independent formation there, 

 does not argue against its interpretation as operculum. In this 

 connection one observes that in Triton and Diemictylus the 

 operculum is formed partly by the cutting-out process and 

 partly by growth of the cartilage into the membrane. The 

 caudal part of this plate in Spelerpes possesses the same rela- 

 tions to parts of the internal ear as the operculum of Ambly- 

 stoma. Furthermore, some time before the formation of car- 

 tilage in the caudal portion, the membrane bulges out in a 

 fashion characteristic of the perilymphatic prominence of the 

 operculum. It should be noted, too, that the extreme cephalic 

 portion of the fenestra is not filled by the plate. This is evi- 

 dent in the drawing of the model (fig. 26). Perhaps a distinc- 

 tion should be made between the cephalic and caudal halves of 

 the plate, but since it is composed entirely of tissue that belongs 

 to the ear capsule itself, the term 'operculum' will be employed 

 for the entire structure less the stylus which is morphologically 

 'columella,' as stated above. To the extent that the stylus at 

 its caudal end becomes joined to the fenestral plate, this single 

 element in Spelerpes represents a fusion of columella and oper- 

 culum. A fusion of these elements in Amblystoma would result 

 in an equal contribution to the plate on the part of both columella 

 and operculum, while in Spelerpes the columella takes no part in 

 the formation of the plate whatever. 



There is a peculiar relation between the sound-transmitting 

 apparatus and the hyomandibular cleft in Spelerpes bislineatus 

 which should be mentioned. This relation exists from the very 

 beginning of the columella to the assumption of terrestrial life. 

 Mention has already been made of the dorsal extension of the 

 hyomandibular cleft throughout embryonic life and its relation 

 to the columellar proton. With the beginning of larval life the 



