580 B. F. Kingsbuiy and H. D. Keed, 



somewhat better understood. Eleven larvae of Spelerpes bislineatus 

 ranging in lengi;h from 15 to 55 mm. were studied by means of 

 serial sections. Just when the columella makes its appearance we 

 can not say, but in larvte 15 and 17 mm. long there is present a deli- 

 cate cord of cells outside the ear capsule extending from the under 

 side of the squamosum towards the fenestral membrane to which 

 it is not closely related at this stage. In a larval Plethodon cinereus 

 (Figs. 6 and 7) of a similar stage of development this cord is 

 composed of a greater number of cells and is consequently more com- 



V.p-Ir 



Col 

 C. 



Fig. 8. Spelerpes bisliueatus, larva 23 mm. long. C, artel-ia carotis 

 Interna ; C.I., canalis lateralis ; CoJ., columella ; G.p., cavum perilymphaticum ; 

 y.p-h, vena petroso-lateralls. 



pact and larger. Here also, as in Spelerpes, this group of cells is 

 not closely connected with the fenestral membrane. It extends for- 

 ward to the under side of the squamosum and apparently is joined 

 to the ceratohyal by a less marked cord of cells. Figs. 8 and 9 

 from two sections 25 microns apart may serve to illustrate the extra- 

 otic position of the columella. Comparison with the figures of like 

 stages of Ambystoma and Cryptobranchus is suggested. 



In Sperlerpes larvse 23 mm. long the lower end of this cord of cells 

 has become intimately associated with the fenestral membrane at 

 the cephalo-ventral margin of the fenestra. At this point the fenes- 



