192 AYERS. [Vol. VI. 



acustica, as Hensen also called it, he found four kinds of cells 

 — {ci) rods, (b) hair cells, {c) elongate peripheral cells (support- 

 ing cells), {d) Corti's and Deiters's cells (Stabchenzellen of Ley- 

 dig, Haarzellen of Kolliker). 



In tracing the development of these parts of the adult Corti's 

 organ in the embryo, Hensen started with the epithelial ridge 

 as the basis of all ; and since in the adult a membrana tectoria 

 had been described, he searched for it in the embryo, but could 

 not find it ; and, considering the methods then in vogue, one 

 is not surprised at his lack of success. 



Hensen concluded that the perforate membrana tectoria of 

 the bird's ear was the analogue of the striated membrana of the 

 mammal ear, and he considered both to be the product of the 

 secretion of the cells of the epithelial ridge. By the growth of 

 the basilar membrane and the lengthening of the rods of Corti, 

 the papilla acustica, or that part of it which represents hair cells 

 of the organ of Corti in the adult, was pushed out under the 

 edge of the tectorial membrane, which by this time had sepa- 

 rated from the surface which secreted it as a permanent gelati- 

 nous mass floating freely, except the attachment of its inner 

 edge, in the endolymph above the short hairs of the hair 

 cells. 



The few facts given above were about all that had been 

 obtained relative to the organ of Corti by the observers down 

 to Boettcher's time. 



Boettcher's great service consists in his having given us 

 a very extended account of the development of the auditory ap- 

 paratus in several species of mammals. The stages he studied 

 were sufficiently close together to allow of tracing all the 

 changes with certainty, and in this way his monograph con- 

 tains the completest and most accurate account of the growth 

 of the mammalian internal ear of any author down to this time ; 

 for Retzius's studies of the development in the Rabbit, Cat, and 

 Man may fairly be considered to be contributions to Boettcher's 

 exposition of the ontogenesis of the mammal ear, as I think 

 the author himself considered them. Retzius confined his 

 embryological studies almost entirely to the ontogeny of the 

 cochlear duct. 



According to Boettcher (31, 1869) the cochlear tube arises as 

 a bulb-like pocket from the sacculus, and soon turns inwards and 



