DEVELOPMENT OF THE MEMBRANA TECTORIA 445 



the spiral sulcus, and in measuring the width of the inner cell 

 group one is including cells which form part of the spiral organ. 

 No accurate comparison can thus be made. The distance be- 

 tween the inner angle of the cochlea and the pillar cells, two 

 definite points, may be measured with considerable accuracy and 

 shows no important change in the position of the spiral organ 

 from the 13 cm. to the 18.5 cm. stage, nor later in the new-born 

 animal. (6) As the basal membrane does not shorten, the dis- 

 placement theory must assume that dead passive structures 

 like the pillars actively move inward over the surface of the 

 basal membrane. 



One argument which Hardesty uses to prove that inward. dis- 

 placement of the spiral organ has occurred is that the 'fibers' 

 of the membrana when traced from' its upper and outer border 

 curve outward, downward, and then inward as though they had 

 been pulled inward by the migration of the spiral organ. This 

 inward curvature of the fibers is only found in the upper turns 

 of the cochlea where the membrana is of greatest width and 

 thickness. It may easily be accounted for. In the stages up 

 to 16 cm. the cells of the spiral organ slant outward but as the 

 width of the basal membrane is rapidly increasing the inclina- 

 tion of the chambers, hence of the 'fibers' is downward and 

 outward. When the membrane begins to develop actively over 

 the spiral organ the basal epithelium has attained its maximum 

 width but as the cells are directed outward the inclination of 

 the chambers will now be inward. When the spiral sulcus is 

 developed by the degeneration of its cells, the outer cells of the 

 spiral organ elongate and straighten somewhat so that they are 

 no longer directed outward. This shifting, which is relatively 

 slight and not enough to account for the displacement of the 

 membrana, would nevertheless increase the inward tr^nd of its 

 chambers. My observations are supported by those of Held ('09) 

 on the guinea-pig and rabbit. 



In taking measurements of the 18.5 cm. stage the marked 

 changes found are : (1) The increase in thickness of the membrana 

 tectoria; (2) The increased distance from the inner angle of the 

 cochlea to the labial teeth. The outer cells of the labium have 



