THE NERVOUS SYSTEM OF AMPHIBIA 261 



upon entering the brain at this stage, although this has not been 

 actually demonstrated in individual fibers. 



2. The visceral sensory component. The geniculate ganglion in 

 its proximal portion holds a relatively ventral position in the 

 ganglionic complex. Distally it reaches ventrad and rostrad to 

 the region of contact between the ectoderm and entoderm of the 

 spiracular pouch, where it becotnes continuous with a cluster of 

 ectodermal cells which has pushed in over the entoderm. This 

 cluster of cells is, presumably, the epibranchial placode of this 

 nerve. No fibers can be seen issuing from the geniculate gan- 

 glion at this stage. The root fibers of the geniculate ganglion 

 are shown approaching the brain in figure 25 (R.VII,vis.) at a 

 distinctly more ventral level than the lateral line root. They 

 turn caudad immediately within the external limiting membrane 

 and form an incipient fasciculus solitarius (figs. 26, 27). Their 

 visible course is limited to the sections figured in this series. 



3. The audilory organ and nerve. The auditory ganglion has 

 become completely detached from the vesicle. In figure 7r>, a 

 single cell {VI 1 1) represents the distal end of the ganglion. 

 Towards the brain from this position the ganglion can be fol- 

 lowed distinctly (fig. 2, G.VIII). The auditory vesicle has 

 detached itself entirely from the skin and has made very per- 

 ceptible progress in dilTcrentiation since the non-motile stage, as 

 may be seen by comparing figures 73 and 75. Mitotic figures 

 are still very abundant in the inner portion of the epithelium. 

 The root fibers of the nerve are seen in figure 27 (R.VIII) enter- 

 ing the brain on the ventral aspect of the root of the geniculate 

 ganglion. In figure 28, taken from the next section caudad of 

 27 (10 m) no descending auditory root fibers can be definitely 

 recognized. 



C. THE COILED-REACTION STAGE 



As in the case of the trigeminal ganglia, the ganglia of the facial 

 complex have become more consolidated towards the brain and 

 around the antero-ventral aspect of the auditory vesicle. 



1. The lateral line component. The lateral fine primordia have 

 become greatly extended since the early flexure stage (Paper I, 



THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 26, NO. 3 



