DEVELOPMENT OF THE ORGAN OF CORTI 289 



nerve bundle, that is to say, between the nucleated portions of 

 the inner and outer rods of Corti (fig. 5, t, T), never ''ungefahr 

 in der Mitte des Zellenhohe," as Retzius asserts and many- 

 investigators illustrate. It is a perinervous space. Later it 

 extends between the intemiediate portions of the pillar cells. 



According to this description, the tunnel space must be held 

 to be a true intercellular cleft, the fluid contents of which are 

 developed by a process of secretion from the neighboring parts 

 of the pillars and a simultaneous partial cytolysis of the latter. 

 The space enlarges at the expense of the cell bodies. In the 

 earhest stages of development of the organ of Corti there appears 

 in the pillars not only a fibrillated sustentacular apparatus 

 related to their function of support, but also a large, clear, 

 vacuolated cytoplasm, the bulk, of their cell bodies. This 

 portion of the protoplasm is glandular in nature, and from the 

 blood plasma of the subjacent vas spirale (fig. 1, vs), it derives 

 its nutritive material, which is elaborated and converted into 

 clear vacuoles. The products of secretion are discharged along 

 with a partial liquefaction of the surrounding cytoplasm. 



During the extension of the tunnel space the superficial seg-- 

 ments of the outer pillars undergo considerable enlargement, 

 and their radial diameters soon correspond to those of the 

 intemiediate portions (fig. 4, ohd). At that time the process of 

 cytolysis obviously extends along these segments (figs. 4 and 5, 

 t), from below upward, involving a rapid reduction of their 

 radial diameters. The intermediate segment of the outer and 

 inner pillars, previously broad and formed of a small fibrillated 

 part and a large vacuolated portion next to the future cleft, 

 becomes gradually converted into a slender band, the so-called 

 'body' of the pillar. In figure 7 (opb) these bodies are shown 

 cut at successive levels through fifteen outer pillars. In their 

 lower portion, as seen in nine sections, they are reduced to thin 

 cylindrical fibrillar strands, part of their apparatus of support, 

 from around which the clear cytoplasm has disappeared. In 

 their upper part, as seen in the next four sections, the pillar 

 bodies are still composed of the original two zones, the vacuo- 

 lated portion having been somewhat reduced. Close to the 



