THE NERVOUS SYSTEM OF AMPHIBIA 255 



verse plane, through the entrance of the trigeminal nerve, the 

 same type of cell appears. In figures 36 and 37 the same cell 

 appears (DC). Its typical, large nucleus has two nucleoli, one 

 in each section. In both sections the peripheral process, which 

 projects into the root, can be distinctly recognized. In figure 

 36 a process runs ventrad towards the motor centers, and in 

 figure 37 there appears the basal portion of a process which is 

 directed dorsad. This structure conforms to the Rohon-Beard 

 cells which, in early stages, have one peripheral process and two 

 central. Figure 35 shows the presence of several other cells of 

 this type in the immediate vicinity of the root. The distinctly 

 more ventral position of the motor nucleus (fig. 36. Xuc.vis.m.) 

 precludes any possibility of confusing motor with sensory cells 

 in this region. In figure 34 there is represented one of these 

 cells which is situated still farther dorsad, and 56 m cephalad of 

 the entrance of the root of the nerve. The long process running 

 ventrad from this cell indicates that it has become unipolar, after 

 the manner of the Rohon-Beard cells in the spinal cord. 



U. THE EARLY SWIMMING STAGE 



In embryos of this stage the ophthalmic ganglion has pressed 

 still farther back upon the root against the brain. It now has 

 a wide contact with the Gasserian ganglion (fig. 4, G.oph.). 

 Cephalad it extends nearly to the rostral border of the eye (fig. 

 78). From the caudal portion of the ganglion there now arises 

 a small nerve which goes dorsad to the skin. In some speci- 

 mens this seems to be represented by a single fiber. It appears 

 as such in silver impregnations. This is probably my ))ranch 'x' 

 of the advanced larva and adult ('02). Near the rostral border of 

 the eye (fig. 4, L.o.p.V), a branch, consisting of only a few 

 fibers, passes laterad around the anterior surface of the eye to 

 a position lateral and caudal of the external nares. This is pre- 

 sumably my lateral terminal branch of the adult ('02, fig. 2, 

 I.o.p.V). The remainder of the nerve passes along the mesial 

 aspect of the olfactory epithelium to the skin of that region. 

 This must be the mCvSial terminal branch of the adult. A con- 



