2o6 AYERS. [Vol. VI. 



reached its permanent condition, and in the main subsequent 

 changes affect its size only. 



The Boettcher cells, which are developed in the bottom of 

 the sulcus spiralis externus, are simply the undeveloped re- 

 mainder of the low epithelial ridge which formerly occupied 

 this region. They disappear after the first month. 



There is no difficulty in harmonizing Retzius's story of coch- 

 lear ontogeny with the views which I have sufficiently set forth 

 in preceding pages, when it is remembered that he has described 

 the appearance en masse of the sensory hairs, the whole mem- 

 brana tectoria as a unit, not having recognized the individual 

 hairs. The same is true of the spiral nerve fibres. 



Hensen showed by measurements on the Ox the amount of 

 translation of these structures during development, and found 

 that the inner cells travelled quite up to the habenula perforata, 

 while the outer row remained (with exception of the apical cells) 

 practically in the same position. Hensen considered this spread- 

 ing or diverging of the pillars of Corti as a process by means of 

 which the hair cells of the small ridge were transported under 

 the membrana Cortii. Middendorp concurred in this view. 

 Boettcher found that the pillar structures moved oittwards. In 

 the adult the space between the feet of the pillars decreases 

 continually from above downward, while in the embryo the 

 space between the feet of the pillars increases continuously 

 from above downwards. 



The inner pillar is at first longer than the outer, then for a 

 time they are of equal size, but soon the outer pillar grows 

 longer and remains so ever after. 



Hensen in 1873 again took up the subject and concluded that 

 the translation of the papilla from without, under the mem- 

 brana tectoria, was fully proven in the case of the Ox. 



In embryos the pillars are perpendicular and close together. 

 The upper end of the arch is inclined outwards. 



Retzius further studied the development of the cochlea in the 

 Cat, selecting the following stages: embryos of 8, 12, and 15 cm. 

 in length, and the new-born foetus, for the embryonic or early 

 development, and the three-days, seven, eleven, and thirty-days 

 old Kittens. He found the development essentially the same 

 as the Rabbit, with the exception that the new-born Cat is much 

 farther advanced than the new-born Rabbit. 



