288 O. VAN DER STRICHT 



sidered as the segment which will become converted into the 

 so-called head of the inner pillar. 



The outlines of all the pillars are very sharp, not only between 

 the cells of the same row, but also between the neighboring 

 elements of the two rows. While at the level of the superficial 

 segments this outline is represented by an intercellular material 

 (figs. 1 and 3, tb), which in its staining capacity and chemical 

 constitution agrees with that of the superficial terminal bars, 

 between the two lower segments of the pillars it is composed of 

 a paler, more fluid, or true intercellular cement, in addition to 

 which a very thin superficial cytoplasmic film can be brought 

 into view. This outline and film are lacking along the axial 

 surfaces of the inner pillars and the lateral surfaces of the outer. 

 The spiral nerve bundle (A^") occupies an intercellular position 

 between the nucleated parts of the outer and inner pillars, some- 

 times encroaching somewhat upon the lower interstice which 

 separates their intermediate portions. The nuclei of the pillar 

 cells are surrounded by vacuolated cytoplasm. The nuclei of 

 the inner pillars are much smaller than those of the outer and 

 much more flattened out radially. 



When the tunnel space is about to appear, there occurs a 

 characteristic alteration in the cytoplasm adjacent to this 

 future cleft, the vacuoles running together and thus increasing 

 in size (figs. 1 and 2, t). A common vacuolated mass soon ap- 

 pears (figs. 3 and 4, t) ; at certain places it remains fused with 

 the cell body from which it is derived, at others it is independent, 

 so that one cannot determine to which of the neighboring pillars 

 it belongs. From this moment there exists a narrow inter- 

 cellular cleft, filled with a small amount of extracellular, vacuo- 

 lated material, a common mass which doubtless represents the 

 first trace of the intratunnelar fluid, and w^hich gradually increases 

 in quantity by the coalescence of adjoining portions, partly in- 

 corporated in the original pillar and partly free or extracellular. 

 Although from the earliest stages of the appearance of the 

 space small extracellular, vacuolated masses can be found between 

 the intermediate segments of the pillars (fig. 4, t), the larger 

 part of the tunnel is generally seen around and close to the spiral 



