52 IRVING HARDESTY 



(2) As seen in the drawings, the spiral organ grows in thickness 

 between the time the tectorial membrane begins to span over it 

 and the adult stage. The greatest increase in thickness occurs in 

 its outer side by the increase in the length of the outer sustentac- 

 ular cells, and the apical ends of these curve axisward. As 

 a result the apical surface of the organ is made to incline axis- 

 ward. The outer pillar of the organ also increases in length 

 more than the inner pillar, and as a result of this, and perhaps 

 of the increase in the length of the outer supporting cells also, 

 the apical ends of the two pillars are forced axisward. At their 

 differentiation, the apical ends of the pillars incline strongly 

 outward (see fig. 8, 19 cm.) in conformity with the pressure of 

 the cells of the outer part of the greater epithehal ridge. It 

 seems evident, therefore, that the apical surface of the organ is 

 forced axisward during growth and therefore under the tectorial 

 membrane to a shght extent. The normal spaces between the 

 elements of the spiral organ, including the large NueFs space, 

 no doubt result in part from this movement of the organ axis- 

 ward. Nuel's space, however, is present in considerable size 

 before the upgrowth of the outer supporting cells has started 

 (compare figures 8 and 2). This space increases in passing 

 from the basal to the apical end. Any movement of the sur- 

 face possibly produced in this way is, however, not enough to ac- 

 count for the change in relative position of the organ evident in 

 the apical turns. In the basal end, the great increase in the height 

 of the outer supporting cells does not occur, thus the apical surface 

 of the organ is not inclined axisward, though, the pillars do not 

 lean outward as might be expected. The change in the relative 

 position of the organ with reference to the basal surface of the tec- 

 torial membrane is less in the basal end and progressively increases 

 in passing toward the apical end. 



(3) To accomplish the very marked shift in the position of 

 the spiral organ with reference to the basal surface of the tec- 

 torial membrane, especially in the apical turns, some process is 

 necessary by which the entire organ is moved axisward. Dur- 

 ing differentiation of its elements, the spiral organ is situated 



