340 



AVERS. 



EXPLANATION OF PLATE II. 



Fig. I. A horizontal section of the ear of Petromyzoji marinus, through the 

 middle of the vertical diameter of the saccular appendix or lagena, showing the 

 bifurcate sense organ of the lagena, and the nerve supply. X 45- c., the cupulas 

 terminales of the sense organs. 



Fig. 2. A vertical section through the posterior ampullar sense organ of the 

 Petromyzon ear, to show the mutual relations of sensory epithelium, canal wall, and 

 nerve. X 140. c.^ canal wall thickened where the nerve penetrates it to enter the 

 sense cells, whose position is indicated by the pink shade, cr.ac, r.ac, and r.ac' the 

 accessory nerve in long and cross section. 



Fig. 3. A transverse section (radial) of the cochlear organ and canal of the 

 Rabbit, to show the usual relation of sensory hair band to the limbus sulcus spiralis 

 in parafhne preparations. *, the region from which Fig. 5 is taken, fi the caps of 

 three hair cells, pulled off and still in connection with the hairs, c.p., Corti's pillars 

 and the remnant of the organ of Corti. tjt.r., membrana Reissneri. s.i., sulcus in- 

 ternis. c.n., cochlear nerve, s.v., stria vascularis, m.b., basilar membrane, v.s., 

 spiral or basilar blood-vessel, k.b., hair band. X 150. 



Fig. 4. Sketch of a section of the net of Loewenberg of the Rabbit in its relation 

 to the sensory hair band. From the region of the lower outer angle of the hair band 

 in such a section as is shown in Fig. 3. r.w., the thickened rim or edge of the hair 

 band known as Hensen's " Randwulst," here seen to be composed of fibres. kJ , the 

 hairs of the outer hair cells. X 1400. 



Fig. 5. A surface view of the net of Loewenberg from the region * of Fig. 3. 

 X 850. The net appears to be composed of cords and threads of varying size, and 

 the meshes are not only unequal, but also very irregular in size and shape, h., un- 

 changed hairs of the outer hair cells. 



Fig. 6. Perspective view of the region f of the section of the hair band shown 

 in Fig. 3, and more highly magnified, c/i.c, one of the caps of the outer hair cells 

 which has remained in its normal attachment to the hair band, and which gives rise 

 to 27 filaments or auditory hairs. X 850. 



Fig. 7. (a) Surface view of the " Randkorpern " or " Randwulst " of the hair 

 band, showing its reticulated structure, and (^b) its relation to the sensory hairs in 

 radial section. The preparation is taken from lo-inch Pig embryo. This appearance 

 is not unusual, but the intermediate stages between this and the condition in which 

 all traces of such structures are absent, as in the living and freshly prepared organs, 

 are also abundant. 



Fig. 8. The macula utriculi and the crista acustica of the anterior ampulla of 

 the Opossum. X 30. 



Fig. 9. Two supporting cells of the Sauropsid organ of the Alligator. X 440. 



Fig. 10. Tangential (vertical) section of the endolymphatic sac of Dasyatis cen- 

 trurtis. X IS- 



