No. I.] THE VERTEBRATE EAR. 6l 



a direct descendant of the organ of Corti as found in the Alli- 

 gator, and for the following reasons : the Sauropsid organ of the 

 Alligator is made up of sensory cells of a different character 

 from those found in the Alligator's organ of Corti. This is 

 especially true of the innermost four or five rows of the organ 

 of Corti. For in these innermost rows the cells are more 

 like those of the organ of Corti in the mammals than those of 

 any other parts of the epithelial ridges, and are very different 

 from the remaining cells of the organ lying outside of them. 



I look upon these rows of modified cells in the Alligator's organ 

 of Corti as the earliest indication of the peculiar and character- 

 istic structures of the organ of Corti in the Mammalia ; and if 

 such is the truth, the latter organ must have arisen entirely 

 from the former. Accepting the other supposition, we should 

 necessarily have to conclude that the arches of Corti arose 

 from the supporting cells of the edges of the Sauropsid and 

 mammalian organs, and that Corti's canal is represented in 

 the Alligator by the deep valley separating these two struc- 

 tures. 



While it is entirely possible for the supporting arcade to have 

 arisen in this way, and although such a method of origin would 

 render some difficult problems much easier of solution, and has 

 thus the factor of simplicity in its favor, it must be said that at 

 the present time the latter view is not so well supported by facts 

 as the former. 



The arch of Corti in the mammalian ear (PI. XII) is located 

 outside of the place of entrance of the cochlear nerve into the 

 cochlear canal, and in the Alligator the relation to the organ of 

 Corti {i.e. the inner four or five rows of modified cells) is very 

 similar, while the relation of the nerve to the Sauropsid organ 

 is very different and of the same nature as that sustained by the 

 cochlear nerve to the large epithelial ridge in the developing 

 mammal. 



The supporting cells of the organ of Corti, like those of all 

 other sense organs of the lateral-line category, comprise all of 

 the non-sensory cells of the ridge-like organ. So far as my 

 observations enable me to decide, these cells are all simple, i.e. 

 there are no twin cells in the sense in which Waldeyer, Gott- 

 stein, and Nuel use the term. Since the supporting cells, with 

 the exception of the double row called Corti's pillars, ate of 



