No. I.] DEVELOPMENT OF THE EAR OF AMBLYSTOMA. 31 



and also separates the sensory area common to the utriculus 

 and ampullae of the anterior and horizontal canals from the 

 sensory epithelium of the sacculus. The utricular sensory area 

 later divides into the macula acustica utriculi and the cristae 

 acusticae of the anterior and horizontal ampullae. At the time 

 of the division of the sensory band into three parts the whole 

 mesal wall of the sacculus is made up of thickened epithelium. 

 But already a differentiation into distinct areas is indicated here. 

 The macula acustica sacculi, the macula ac. neglecta, and the 

 papilla ac. lagenae appear as thickened areas in the wall of sen- 

 sory epithelium. The macula ac. neglecta is the first of the 

 three to become isolated, in the manner already described. 

 The papilla ac. lagenae is connected by the thickened columnar 

 epithelial walls of the lagena with the macula ac. sacculi till 

 the adult condition is nearly attained. In later larval stages 

 a fourth sensory patch of the saccular region makes its appear- 

 ance differentiated from the dorsal wall of the lagena. This is 

 the papilla ac. basilaris. 



It is thus seen that from the primary utricular region are 

 developed three sensory patches : the cristae of the anterior 

 and horizontal canals and the macula of the utriculus. From 

 the sacculus develop five sensory patches : the crista of the pos- 

 terior canal, the macula ac. neglecta, the macula ac. sacculi, the 

 papilla ac. lagenae, and the papilla ac. basilaris. The relations 

 of these nerve end-organs in various stages of development may 

 perhaps be rendered clearer by representing them as projected 

 on a plane surface. Fig. 21 represents the outline of the sen- 

 sory area in larvae of about 9 mm. in length. Fig. 22 shows 

 the indications of a division into utricular and saccular portions. 

 Fig. 23 shows this still more clearly, and now the separation of 

 the posterior ampullar sensory area has begun. The lagenae 

 becomes outlined. In Fig. 24 is seen the division of the origi- 

 nal continuous band into three parts, and the relations of these 

 parts to each other. The positions of the pars neglecta and the 

 lagena with respect to each other are indicated. Fig. 25 shows 

 the pars neglecta and lagena as more widely separated. In Fig. 

 26 the utricular sensory area has completed its division into 

 three parts. The pars neglecta is 'distinct from the sacculus, 

 and the papilla ac. lagenae is soon to become isolated. Fig. 27 

 represents the adult relations of the nerve end-organs. The 



