10 



AYERS. [Vol. VI. 



are entirely absorbed, in which case the lining epithelium would 

 be equivalent to the " Ersatzzellen " of Ketel (in Petromyzon), 

 or it may as well be that the long columnar cells are simply 

 reduced, on account of decreased nutrition, and appear as 

 cubical or spherical cells. No explanation has yet been offered 

 of the apparent fact that there are no small surface hair cells 

 in the Sauropsid organ in the developing mammal such as exist 

 alone as the sensory elements (i*) in the hydrosauria. Where 

 are these short cells or what represents them .'' How many 

 of the long epithelial cells in the embryo mammal bear hairs, 

 and where are the supporting cells at this stage .'' 



13. The so-called membrana tectoria of previous authors is 

 in reality a hair band or field of long slender hairs which spring 

 from the tops of the hair cells and form a waving plume on the 

 crest of the ridge of the organ of Corti. Each hair cell gives 

 off a bundle of about two dozen hairs which spring from the 

 whole surface of the cell cap (Didelphys, Mus, Bos, Sus, Homo), 

 and each individual hair floats freely in the endolymph. 



14. The membrana tectoria, the membrana reticularis, Loe- 

 wenberg's net, and the three or four main trunks of the system 

 of spiral nerves of the cochlea have no existence as such in the 

 living mammalian ear, the first of them being the chemically 

 and physically modified hair band ; the second one being an 

 artifact produced by the separation of the cell caps of the organ 

 of Corti from their cells, in the form of a continuous and more 

 or less perforated plate ; the third structure being likewise an 

 artifact produced by chemical and physical agents in ever-vary- 

 ing form ; while the fourth one of the artifacts mentioned is in 

 all probability the product of the transformation of the walls of 

 a lymph space with adherent and included nerve fibres, cell 

 processes, and cell remnants. 



15. The cochlear nerves end in the hair cells and not freely 

 between them, and they are probably continuous with the audi- 

 tory hairs, as Hasse claimed, and as my own observations render 

 almost certain. The continuity of the hairs with the nerve 

 fibres is established by the protoplasmic ways inside the hair 

 cells, which I have designated the capillo-nuclear and the nucleo- 

 neural filaments. Free nerve ends do not exist in the auditory 

 epithelium, and consequently Helmholtz was entirely wrong in 

 ascribing to the auditory otoliths the function of tetanomotors, 



