Plate I. 



Models of the ear region of the skull of Ambystoma punctatum, drawn 

 from the side and slightly from the caudal and ventral aspects. 



Fig. 22. Ambystoma punctatum, mature larva about 45 mm. in length, 

 beginning transformation, gills about one-half absorbed. 



Fig. 23. Ambystoma punctatum, about 42 mm. in length, transformation 

 period, gills mere stumps. In comparison with Fig. 22, there is shown the 

 partially formed operculum with the opercular muscle. 



Fig. 24. Ambystoma punctatum, young adult, about 52 mm. in length. 

 The columella is now nearly completely fused. Remnants of the secondary 

 fenestra are marked "F." Operculum and opercular muscle. 



