294 O. VAN DER STRICHT 



a cubical or prismatic shape, the larger base of which touches 

 the surface of the organ of Corti, its tapering apex blending 

 with the much smaller pillar body. In cross-sections the prism 

 is square or quadrangular in shape. 



During this process of enlargement of the head, many re- 

 markable changes occur. 1) A considerable shortening of the 

 head segment (fig. 7) as if the compact substance of the lower 

 parts had been pushed upward. Moreover, there can be no 

 doubt that, at the same time, the vacuolated cytoplasmic zone 

 of the intermediate portion of the pillar extends upward along 

 the primitive head, so that the pillar body becomes longer at 

 the expense of the latter. 2) A peculiar transformation of the 

 protoplasm of the heads of the outer and inner pillars, close 

 to and through the agency of the obturator septa. Primitively 

 compact, homogeneous, or granular, entirely different from the 

 vacuolated or fibrillated cytoplasm above referred to, the pro- 

 toplasm of the head becomes converted into a denser material, 

 staining intensely with iron hematoxylin. These changes occur 

 in succession, first within the heads of the outer (figs. 4 and 7, 

 ohd), then within those of the inner pillars (fig. 8, ihd), in 

 proximity of the obturator septa separating their apical from 

 their basal surfaces ; later, along the medial surfaces of the heads 

 of the outer pillars, and finally ^long the lateral surfaces of the 

 heads of the inner pillars, close to the obturator partitions which 

 separate these two elements (fig. 9, ohd and ihd). In sections 

 tangential to the surface of the organ of Corti these altered 

 cytoplasmic portions are seen in the form of deeply staining 

 uniform, planoconvex masses, the planar surface of the clump 

 of one head adjoining that of another mass belonging to a con- 

 tiguous head (fig. 11). In reality, each planoconvex clump is 

 the section of a vertical band or semicolumn. Thus in each 

 head there appear three semicolumns, which at first are separated 

 from one another, but in more advanced stages Coalesce to fonn 

 a single band or imperfect collar open toward the side of the 

 head where the obturator material is lacking (figs. 7, 8, and 9). 

 What mechanical factors cause these structures to appear is 

 uncertain. It can only be stated that this dense and horny- 



