62 AVERS. [Vol. VI. 



interest mainly from the histological standpoint, I shall not 

 enter into a detailed account of them here. Suffice to say that 

 they are of various sizes and shapes, depending upon their posi- 

 tion in the sensory ridge, and they pass over into the indifferent 

 epithelial lining, of the sulci internus and externus. The rods of 

 Corti are of unusual interest, since they make their appearance 

 among existing forms only in the Mammalia. In the Mono- 

 tremes, where the cochlea retains a lagena, its main Sauropsid 

 character, the arches of Corti are already well developed, and 

 we must look for their early stages of growth and development 

 among extinct forms of the Post Reptilia. The story of their 

 development will be given further on ; but when once matured 

 they constitute the long tent-like cover or inclosure of the canal 

 of Corti. Each rod is composed of a large number of isolable, 

 fine, transparent threads, of circular section. The minute hya- 

 line cylinders conform to the curvature of their rod. The whole 

 bundle is inclosed in a cell which for the greater part of its 

 length fits it closely like a sleeve, while at its foot and some- 

 times at its head the remaining protoplasm of the cell is col- 

 lected. The cell nucleus, which persists throughout the life 

 of the rod, lies always in the foot on the tunnel face of the rod. 

 The fibres of the two rods opposite each other seem to blend 

 at their union above, thus forming the keystone of the arch. 



From here they diverge until they come in contact with the 

 basilar membrane, when they turn suddenly outwards, i.e. away 

 from the tunnel, and run parallel with the fibres of the basilar 

 membrane, among which they sometimes, appear to be rooted; 

 and Nuel was led by this appearance to figure and describe a 

 continuity of the pillar fibres with those of the basilar mem- 

 brane. I am convinced such does not exist. 



The cell caps of the cells forming the ridge of Corti are 

 fused together,^ thus forming a continuous sheet, and the pillar 

 heads form a broad, smooth band, marked only by transverse 

 and parallel lines, which, throughout the length of this plate, 

 divide it into inner and outer halves, and these into segments 

 (PI. Ill, Figs. I and 7; PI. IV, Fig. 6; PI. V, Figs, i'^ and 10; 



1 While in the living condition the caps of the epithelial cells are in close contact, 

 in hardened preparations they are more or less soldered together by the action of the 

 reagents, and their continuity is thus mechanical and not organic. They do not differ 

 in this respect from other forms of epithelial cells. 



