5o AVERS. [Vol. VI. 



origin and development. These hair cells do not vary much in 

 their characters in domestic animals. This row is the most 

 complete of the several rows of the organ, and it shows super- 

 numerary cells less often than the other rows. In histological 

 details the cells are quite unlike those of the outer rows, and, 

 according to Retzius, they approach those of the maculae utric- 

 uli and sacculi in their shape, size, and structure. They are 

 entirely filled with a dark, coarsely granular protoplasm, and 

 consequently lack the clear end space of the cells of the outer 

 rows. The hairs appear to be better developed than in the case 

 of the cells of the maculae. 



According to Gottstein and Waldeyer, and Retzius agrees with 

 them, the inner row of hair cells is developed from the outer- 

 most cell of the large epithelial ridge ; but according to Boettcher 

 the innermost cell of the small ridge gives rise to the inner hair 

 cell. It becomes a matter of great importance for the correct 

 understanding of the organ of Corti to determine the source of 

 all its elements. For my own part I am fully persuaded that 

 the inner row of hair cells arises entirely within the bounds of 

 the small epithelial ridge, and the evidence is not merely embry- 

 ological, as derived from the study of mammalian development, 

 but comparative anatomical, based on the study of the organ of 

 Corti in the Alligator and several mammalian ears. Allowing 

 that the inner cell is developed from the outermost cell of the 

 large epithelial ridge, we should have to separate the organ of 

 Corti into two very distinct portions, one of which would in- 

 clude the portion supplied by the Sauropsid organ, i.e. the 

 inner row of hair cells, and its supporting cells, or the inner 

 row of Corti's pillars; while the other one would include the 

 rows of the outer hair cells and the outer pillars of Corti. 

 While my own observations on the ontogeny of the ear agree 

 with Boettcher's, they are not sufficient to warrant at this time 

 a final conclusion as to the part actually played by the Sau- 

 ropsid organ in the adult mammalian ear. As I have said 

 before, I think it disappears as a sense organ, being repre- 

 sented in the adult mammal only by the lining epithelium of 

 the sulcus spiralis internus. 



The structure of the Sauropsid and mammalian organs as 

 they exist in the Alligator is such that I am inclined to think 

 the whole of the organ of Corti as it exists in mammals is 



