AND HAIR-CELLS IN THE DEVELOPING ORGAN OF CORTI. 123 



that are pushed out from a mixed spiral row, or from beneath the hair-cell, into a 

 new space. If this view is correct it must be recognized that the membrana reticu- 

 laris undergoes a process of extension somewhat different from that of the membrana 

 basilaris. It is a well-known fact that the development of the spiral organ of Corti 

 proceeds from the base of the cochlea towards its apex and the sense epithelium may 

 be well develope din the third turn, while in the second it is still in process of differ- 

 entiation, and as yet undifferentiated in the first. Moreover, it has already been 

 mentioned that during the first stage of development the growth and enlargement 

 of the hair-cells, hence of the superficial two-thirds of the epithelium, are more 

 marked than that of the cell bodies of the sustentacular elements constituting the basal 

 third of the epithelium. From this it is evident that the farmer, and its superficial 

 membrana reticularis, extend more rapidly than the latter, not only towards the 

 lateral side of the organ of Corti, but also in a spiral direction from the third turn 

 toward the second, and from the second toward the first; that is to say, from points 

 where the pressure is high to places where it is lower. According to this principle 

 it is not surprising that during the first stage of growth of the organ the apices of the 

 Deiters cells precede their bases in extending toward the apex of the cochlea, so 

 that the deeper part of the cell remains behind three hair-cells, crossed by the 

 phalanx process. 



The second stage of growth, characterized by the peculiar arrangement of the 

 cells of Deiters, lasts a long time, and many other important transformations occur 

 before the final, third stage is reached. The tunnel space between the rods of 

 Corti may appear, but it is noteworthy that the definite arrangement of the outer 

 supporting cells, which is peculiar to the third stage, may be attained before any 

 formation of a tunnel space (fig. 9). 



The most important role in the production of the third stage of development is 

 played by the cells of Deiters, chiefly by their extension in length. During the first 

 and the beginning of the second stage the sensory elements undergo a rapid increase 

 in size and attain their full volume. Afterwards the nucleated body of the Deiters 

 cell becomes gradually longer, as illustrated in figures 7, 20, 19, 19', 14, 15, and 16 

 (d', d", d'") . In earlier stages (figs. 1,2,3 and 4) their nuclei, like those of the rods of 

 Corti (op, ip) are situated close to the basilar membrane, and the nucleated cell body 

 is very short. Later (fig. 19) it gradually extends and soon attains about the length 

 of the acoustic elements (fig. 21, d', d", d'"), its nucleus becoming farther removed 

 from its base (figs. 19 and 19', d', d", d 1 "), reaching its top rather abruptly (figs. 20, 

 21, d', d u , d iu ). Finally, when the nucleated body of the Deiters cell attains two- 

 thirds (figs. 16, 15, d', d u , d ui ) or more (fig. 23, d 1 ) of the thickness of the epithelium, 

 its superficial cytoplasmic end appears to lengthen out more rapidly than its deeper 

 parts and to give rise to a very important segment of the cell, which, for the sake of 

 its physiological function, may be termed the supporting segment, within which a 

 peculiar framework or sustentacular apparatus makes its appearance, the nucleus 

 occupying about the middle (fig. 16) or lower part (fig. 23) of the superficial one- 

 third of the cell body. 



