Some aspects of structural organization in the cochlea of the bat, Pteronotus parnellii.

The scanning electron microscope was used to study some specific features of the organ of Corti in the bat, Pteronotus parnellii parnellii. The region of the outer tunnel and the external sulcus were analyzed in detail. Good visualization of the geometric arrangement of the external sulcus cells and the deep channels for their root processes was obtained by digestion of fixed material with 1% trypsin. Processes of the cellular elements forming the roof of the outer tunnel are very thin and appear to be weakly attached to the heads of the phalangeal processes of the third row of Deiters' cells. In much of the overstimulated and trypsin digested material the weak junction was broken and the outer tunnel elements exposed. Two distinct cellular elements occur along the outer wall of the tunnel. One type has a surface with numerous projections on tis outer tunnel surface. The other has a smooth surface and an expanded fanshaped extremity which forms at least part of the roof of the tunnel. With trypsin digestion some of the more deeply situated cells were exposed.