AND HAIR-CELLS IN THE DEVELOPING ORGAN OP CORTI. 119 



the surface, where they join their apex, the stationary phalanx, interpolated in 

 the lamina reticularis. 



The cells of Deiters of the third row (figs. 2 and 3, d iu ) are four-sided prismatic 

 elements. In tangential section their nucleated basal portions form a nuclear col- 

 umn situated obviously outside of the third outer sensory row, and their superficial 

 cytoplasmic processes are seen as a column of clear, superposed fields often some- 

 what flattened by the enlarged neighboring hair-cells. In figure 2 (d i!i ) their number 

 is apparently the same as that of the cells of Deiters of the second row, but in the 

 bat, according to N. Van der Stricht, there are two cells of Deiters in the third row 

 for each one in the second row. Views from the surface of the membrana reticularis, 

 as illustrated in figs. 10, 13, and 18, enable one to compute the apices of these cells 

 (d ui ), and prove that the cells of Deiters of the third row, if not double in number, 

 are at least always more numerous than those of the second or first row. 



The above-described seven spiral rows of the organ of Corti in the earliest stage 

 of development can be distinctly seen in views of the surface of the membrana 

 reticularis. As illustrated in figure 10, the arrangement of the apices of all the 

 supporting and hair-cells is indisputably along seven spiral rows, each sharply 

 demarcated. These rows are of two different types. The second row of inner 

 sustentacular cells (is"), the row of inner pillars (ip), and the third row of Deiters 

 cells (d ul ), are purely sustentacular in character; while the others the inner (ih, is'), 

 and the three outer rows (op, oh 1 ; d 1 , oh"; d 11 , oh iu ) are mixed rows, supporting and 

 sensory in character. At a slightly more advanced stage of development, however, 

 this primitive condition changes (figs. 3 and 4), the structures assuming a definite 

 arrangement (fig. 18) except for the apices of the pillar-cells, as seen in figure 13. 

 The chief transformation, as compared with figure 10, consists in the appearance 

 between the three mixed spiral outer rows of two interstices belonging entirely to 

 supporting fields. The first is composed of parts of the apices of two varieties of 

 cells, alternately the outer and the inner extremities of the phalanges rf the respec- 

 tive outer pillars (op) and the cells of Deiters of the first row (d 1 ) ; and the second 

 interval is of a similar pattern, alternately the inner and outer extremities of the 

 phalanges of the respective cells of Deiters of the first and second rows. The sen- 

 sory fields are not altered. The supporting fields, or the phalanges, undergo an 

 elongation and extend over the two interstices appearing in the depth of the epithe- 

 lium. The apices of all the cells remain in situ, but the phalanges become elongated 

 and cover parts of two developing supporting interstices. 



SECOND STAGE OF DEVELOPMENT. 



This stage is characterized chiefly by the shifting of the nucleated portions of 

 the outer pillar and outer supporting cells inward and toward the axis of the cochlea, 

 so that, as shown in figures 5, 6, and 7, the basal part of the outer pillars (op) is 

 found to be entirely inside of the first row of outer acoustic elements; that of the 

 first row of Deiters cells (d'), inside of the second row of acoustic elements; that of 

 the second row of Deiters cells (d"), inside of the third row of acoustic elements; and 

 that of the third row of Deiters cells (d ui ) either partially or almost entirely beneath 



