No. I.] THE VERTEBRATE EAR. 43 



Retzius figures as products of the maceration process, perhaps 

 of both reagents and manipulation, and I am confident that the 

 nerve fibres which this author finds between the hair cells, or 

 rather in situations such that he thinks they lay normally be- 

 tween the cells, do not have this relation to the living hair cells. 



TECTORIAL MEMBRANES. 



Alligator (PL IX, Figs. 3 and 4). 



The membrana Cortii (tectoria) in fresh condition is a soft 

 structure which is greatly contracted by alcohol, but is well pre- 

 served in dilute glycerine to which a trace of osmic has been 

 added, after which reagent it appears striated from base to 

 upper surface. It is clear as glass, and it is honeycombed by 

 irregular canals in all its parts. It is applied to the whole of 

 the surface of the basilar papilla. Its transection at any point 

 resembles in shape the cupula terminalis of an ampullar organ. 

 The lower surface of the membrane near the middle line shows 

 the most and largest pores. In ordinary preparations the mem- 

 brane appears to be fixed by its inner edge to the large epithelial 

 ridge, and from here to extend freely out over the surface of 

 the organ, roofing over the groove between the large and small 

 epithelial ridges, but coming to an end before reaching the 

 outermost hair cells. 



The horseshoe-shaped membrana tectoria of the lagena is 

 composed of a dendritic network of many homogeneous fibres. 

 Masses of otoliths are inclosed in the meshes, especially in the 

 upper part of the structure. Retzius describes it as a tolerably 

 thin horseshoe-shaped otolithic mass, containing larger crystals 

 than are found over any other sense organs. 



In the sacculus the otolithic accumulation nearly fills the 

 chamber without showing any specially well-developed mem- 

 brana tectoria. Retzius failed to find the latter. The hairs are 

 present, however, and lie close to the tops of the sensory cells. 



Mimus. 



In the Mocking-bird I have always found the hair plate of 

 the cochlear organ in osmic acid preparations and always free 

 of otoliths. Its structure is shown in Fig. 10, PL VII. The 



