DEVELOPMENT OF THE ORGAN OF CORTI 291 



usually filled with a clear unifomi fluid, which seems to arise 

 from a more active, true secretion. This secretion may continue 

 even in the adult organ, for, according to all the investigators, 

 the nucleus of each pillar cell is surrounded by a clear cytoplasm 

 which extends over the floor of the tunnel. This protoplasm is 

 vacuolated and represents the rest of the original bulky, glandu- 

 lar portion of both sustentacular and secreting cells. 



Development of the heads and the cephalic appendages of the pillar 



cells 



According to the results published in a previous paper (now 

 in press) and those obtained by N. Van der Stricht, at the 

 earliest stage of the development of the organ of Corti the outer 

 pillar cells are located within the first spiral row of outer hair 

 cells, and their superficial segments occupy interstices between 

 two neighboring acoustic elements. By the rapid enlargement 

 of the latter, these superficial elements are pressed out of the 

 row and pushed towards the inner pillars, although their apices 

 remain fixed between those of the hair cells. From this tune the 

 inner and outer rods of Corti constitute a scaffolding, which is 

 made up of two spiral rows of sustentacular elements and is 

 triangular in shape on vertical section. The rapidly enlarging 

 base of the triangle abuts against the basilar membrane, and 

 the apex is interpolated within the superficial membrana reticu- 

 laris, separating the apices of the supporting and sensory 

 elements of the inner spiral row from the apices of those of the 

 first outer spiral row. In a section tangential to the organ of 

 Corti the summit of the scaffolding is represented by a spiral 

 row of very narrow fields, the apices of the inner rods of Corti, 

 separated from one another and from the neighboring fields of 

 the reticular membrane by deeply staining terminal bars, which 

 extend into the d^pth between the superficial portions of the 

 inner and outer pillar cells. Each of these narrow fields contains 

 a diplosome, and will gradually enlarge by a process of com- 

 pression from the underlying expanding heads of the outer 

 pillars. 



