AND HAIR-CELLS IK THE DEVELOPIKG ORGAN OF CORTI. 131 



The superficial mitochondrial body is closely connected with another allied 

 structure the superficial " cuticula"- from which the hairs arise, and which appears 

 to be a center of mitochondria, developing probably around an accessory centro- 

 some and capable of supplying the cuticula with chondriomites. The superficial 

 plate of the acoustic elements from which the hairs arise is mentioned by Retzius 

 (1884) as "ein ausserst diinnen Hautschicht," the inner surface of which is beset by 

 "beim Kaninchen dicht, bei der Katze und dem Menschen mehr zerstreut, sehr 

 feine, gleich grosse Korner" (p. 366). It is termed " Kopfeinlage " by v. Spee, 

 "Haarplatte" by Held (1909), and "cuticula" by N. Van der Stricht. At the 

 surface of the cuticula the latter author describes an "implantation plate or implan- 

 tation crescent," which gradually gives rise to a cone of fibrils or hairs. Although 

 this crescent is closely connected with the diplosome, it is not formed by the central 

 corpuscle, but is derived from the cuticula. Hence the sensory cell is to be regarded 

 as a ciliated but not a vibratile element. It is worthy of note that Fiirst (1900) , many 

 years before, had seen at the surface of the hair-cells of the crista and macula acustica 

 in an embryo salmon aged 90 days, a disc deeply stained by iron hematoxylin, 

 which seemed to be composed of granules ("Basalkorperchen"), centrosomic in 

 character, from which arose the cilia or hairs. Hence Fiirst regards the hairs as 

 specialized, differentiated vibratile elements. 



In most preparations the superficial cuticula of the acoustic elements is seen in 

 the form of a homogeneous plate which intensely stains dark blue, like the hairs, by 

 iron hematoxylin (fig. 4, oh 1 , oh", oh m , ih). On tracing the mitochondrial struc- 

 tures from the level of the nucleus toward the cuticula (figs. 4 and 9), the chondrio- 

 mites are found to be more and more condensed and numerous, running close to the 

 surface and giving rise to a superficial circular plate. This plate covers the largest 

 part of the apex of the cell, leaving space within a notch on its lateral border for the 

 diplosome (fig. 3) . This mitochondrial cuticula usually appears homogeneous and 

 uniform, although in some specimens obviously granular in structure (fig. 9, oh 1 , 

 oh u , oh m ), and in a few selected preparations the arrangement of the mitochondria 

 into granular filaments (true chondriomites) is conspicuous. This is best illus- 

 trated by figure 12, showing a series of inner hair-cells (ih) cut transversely at suc- 

 cessive levels near their apices, so that from right to left one sees three superficial 

 granular crescents, or the cilia or implantation plates; three dark, circular, granular 

 cuticulse, with the neighboring central corpuscle, and within the second cuticula 

 three radiating chondriomites; three masses composed of still deeply stained, coarse 

 granules, situated directly beneath the cuticula; and three finer, granular fields of 

 finer mitochondria of a somewhat deeper portion of the superficial cytoplasm of the 

 acoustic elements. Such figures justified the statement in a previous paper (1918, 

 p. 63) that "this proves that cuticular formations belonging to the first series men- 

 tioned above (p. 57) may be of mitochondrial origin, but in addition it is a striking 

 proof of the mitochondrial nature of the acoustic hairs formed by this plate." 



In other specimens where the mitochondria are also brought prominently into 

 view by suitable fixing agents and stains, mainly by the mixture of formalin and 



