444 C. W. PRENTISS 



In the apical turn, by comparing with figure 4 it will be seen 

 that the membrana is but little thicker over the labium vestib- 

 ulare, is much thicker over the inner cell group and thickest 

 over the spiral organ where, in the 13 cm, stage, it was just 

 beginning to develop. It extends far beyond the outer support- 

 ing cells. In the second turn the membrana is not so thick 

 over the spiral organ but still extends beyond the outer hair 

 cells. In the basal turn the membrana is thickest over the 

 spiral sulcus and extends as far as the outer hair cells. In the 

 two upper turns the membrana seems to be firmly attached to 

 the cells of the greater epithelial thickening and to those of the 

 spiral organ except along its outer zone where it show^s sighs of 

 having shrunken and pulled away. In the basal turn the outer 

 half was free but this also showed the effects of shrinkage and 

 distortion. 



Hardesty has suggested that there is a displacement of the 

 spiral organ when the spiral sulcus is developed, thus accounting 

 for the position of the membrana over the spiral organ in the 

 later stages of its development. 



There are a number of facts which make this hypothesis 

 untenable: (1) Sections and dissections of the 13 to 15 cm. stages 

 show that the membrana is developed over the cells of the spiral 

 organ. (2) In the 18.5 cm. stage the membrana projects further 

 beyond the spiral organ in the apical turn where the differen- 

 tiation of the spiral sulcus has only just begun, and least in the 

 lower turn where the spiral sulcus is fully developed. (3) The 

 distance of the pillar cells from the inner angle of the cochlea 

 (the only definite points which may be taken for comparative 

 measurements) is about the same in the 13 cm. and 18.5 cm. 

 stages. (4) The total width of the thickened portion of the 

 membrana is about one-fourth greater in the 18.5 cm. stage than 

 in the 13 cm. showing that growth has taken place along its 

 outer border. This growth must have been supplied by the 

 cells of the spiral organ. (5) To show that displacement takes 

 place Hardesty measured the floor of the spiral sulcus and com- 

 pared with the width of the inner cell group. There are no 

 definite points which may be taken for measuring the floor of 



