EXPLANATION OF PLATES III-IX. 



A series of microphotographs to illustrate particularly the morphological 

 relations of columella and operculum, from sections through the ear region. 



Plate III. 



Fig. 29. Ambystoma punctatum, adult. Section through the stilus colu- 

 mellae, showing the columellar ligament and its relation to vein and facial 

 nerve. 



Fig. 30. The same. Section farther caudad. The fused columella is ex- 

 ternal to the cephalic end of the operculum. 



Fig. 31. Ambystoma punctatum, larva, early transformation. There is 

 shown columella and the floor of the ear capsule to become operculum. Com- 

 pare with Fig. 32. 



Fig. 32. Ambystoma punctatum, transformation period. The operculum 

 is, at this level, separated from the floor of the ear capsule. 



Fig. 33. Ambystoma punctatum, larva, 35 mm. in length. It shows the 

 columella, stilus, squamoso-columellar ligament. Note the relation of the 

 vein and artery in this and the two preceding figures. 



Fig. 34. Chondrotus tenebrosus, larva. Note the massive stilus articu- 

 lating with the squamosum and its relation to artery, vein and nerve. 



