The Columella Aiiris in Amphibia. 587 



terranean life where a wedge-shaped form is more convenient for 

 making progress in narrow quarters. 



Miss Ellen Tucker Emerson, 2d ('05), states in substance that 

 the operculum is not connected with the suspensorium, and her figures 

 show a short stilus, labelled columella, projecting freely from a 

 basal portion in the fenestra vestibuli called operculum. Serial sec- 

 tions and the model of the specimen studied by us show that the 

 columella is morphologically connected with the suspensorium but 

 interrupted. On the right side of our specimen the stilus begins to 

 grow smaller in diameter a litle beyond the middle of its extent and 

 finally disappears for a distance of 210 microns. Then it appears 

 again, gradually assuming its normal diameter, and continues unin- 

 terruptedly to the suspensorium. Here it is joined to the squamosum, 

 the OS quadratum and the palato-quadrate (PI. II, Fig. 28). 

 Between the free ends of the segments is a well defined ligament 

 within which a few cartilage cells are found at intervals. 



On the left side there are three segments (PI. X, Fig. 68) pro- 

 duced by two interruptions. One of these corresponds in position 

 and extent with the single interruption on the right side. The second 

 occurs just before the stilus joins the suspensorium and is about the 

 same in extent as the first. On this side the distal or third segment 

 extends for a distance along the ventral edge of the squamosal, join- 

 ing the edge of the os quadratum as well, but without relation to 

 the palato-quadrate. It should be noted in this connection that Kings- 

 bury ('03) described the stilus in adult Spelerpes as connected with 

 a rod of cartilage lying along the ventral edge of the squamosum, 

 a condition similar to what is found on the left side of our specimen 

 of Typhlomolge. 



It may be questioned whether the interrupted condition of the 

 stilus in Typhlomolge results from tension and a consequent separa- 

 tion of what otherwise would remain, as developed, a continuous 

 bar of cartilage, or is reminiscent of the condition found in the frog 

 where there are separate centers of chondrification. It should be 

 recalled, however, that in the urodeles where development has been 

 studied, chondrification of the stilus and columella is continuous. 

 Furthermore it is to be noted that in the Plethodontidse there is a 



