352 



AYERS. 



EXPLANATION OF PLATE VIIL 



Fig. I. A transverse secuon of the head of Torpedo 7narmorata through the 

 auditory region, showing the relation of the endolymphatic duct to the auditory invo- 

 lution and the surface of the body. X 85. ch., chorda dorsalis. car., carotid artery. 

 7nd., medulla, d.e., ductus endolymphaticus. a.v., auditory vesicle. Embryo i| cm. 

 in length. 



Fig. 2. A transverse section of the end of the endolymphatic duct taken from 

 the same series as Fig. I, but caudad of Fig. I, showing the manner in which the ear 

 canal opens on the surface of the body, sp., tissue above the superior lip of the duct 

 (primitive opening of the involution of the ear), c.c, connective tissue cells, ect., 

 unmodified ectoderm. X 540. 



Fig. 3. The same, from the next section, o.de., mouth of the duct. X 380. 



Fig. 4. The same, from the section next behind Fig. 3, showing the wide-open 

 mouth of the ear duct. X 285. 



Fig. 5. Surface view of the basilar membrane of the Virginia Opossum, to show 

 its composition, b, m, f, h, the transverse fibres of the membrane. b, in, f, I, 

 the longitudinal fibres above and below the former, which is in consequence the 

 middle layer. The superficial layer of longitudinal fibres is the layer figured and 

 described in part by Nuel, Deiters, and others as one of the bundles of longitudinal 

 nerve fibres of the organ of Corti. X 1065. 



b. Some of the longitudinal superficial fibres. X 850. From another part of the 

 same ear. 



Fig. 6. Surface view of the keystone of the arch of Corti and the pillar head pro- 

 longations, h.o.p., o.h.c, the hair cells of the outer series, i.ch , of the inner 

 series, s., spaces between the pillar heads. From the Opossum. 



Fig. 7. A few isolated superficial longitudinal basilar membrane fibres, or so- 

 called longitudinal nerve fibres of Deiters. X 1065. 



Fig. 8. A small segment of the hair band from the ear of an adult Virginia 

 Opossum. X 380. The figure shows the appearance of the atifacts, or so-called 

 " Rand Korper " of Hensen, and the " Net of Loewenberg." /i.b., hair band. 

 L.n., net of Loewenberg. C.p., Corti's pillars, r.k., " Rand Korper." 



Fig. 9. A single hair cell of the outer series from the ear of an adult Virginia 

 Opossum. To show the relation of the hairs to the cap of the cell. X about 1400. 



Fig. 10. Surface view of four of the inner and four outer pillar heads from the 

 Opossum's ear. X 1400. 



a.c, arch of Corti. i.p. and o.p., inner and outer pillar heads. 



Fig. II. A transverse section of the sense organ in the larger surface canal of 

 Petromyzon marinus. X 165. 



Fig. 12. The nerve end in an epithelial (hair) cell from the same. X about icoo. 



