262 G. E. COGHILL 



fig. 58). In addition to the priniordia shown in the latter figure 

 there is now a priniordium which runs mesad from the base of 

 the balancer on the ventral surface of the head. In this epi- 

 thelial thickening there is a lowly differentiated lateral line organ 

 at the mesial end and possibly another at the base of the balancer. 

 This primordium is not connected with the other preauditory 

 priniordia, unless it is by a very slight ectodermal thickening of 

 an indifferent nature. 



The lateral line ganglia a and h are in close contact with each 

 other proximally but project distally into distinct gangha (fig. 3, 

 G.L.L.VII,a,b). Ganglion a still reaches almost to the skin. 

 In its distal portion it still has two parts, from each of which 

 arises a nerve. These nerves follow the priniordia closely attached 

 to the skin for a considerable distance. The finer divisions have 

 no sheath cells and their exact length is therefore difficult to 

 determine. Ganglion b projects ventrad behind the spiracular 

 pouch and from it nerve fibers pass to the skin at or near the 

 lateral line primordium which has been -described as occurring 

 in this stage at the base of the balancer. 



The roots of the lateral line ganglia enter the brain as illus- 

 trated in figures 38 to 41, figure 38 being the most rostral of the 

 series. Here the root fibers of ganglion b {R.L.L.VII,b) are 

 entering the brain and collecting into a bundle immediately 

 beneath the external limiting membrance. In figures 39, 40, 

 and 41, the next successive sections caudad, the root fibers of 

 ganglion a are entering in a more dorsal position {R.L.L.VII,a). 

 Within the brain these fibers appear to bifurcate. At least they 

 form short ascending and descending tracts as shown in figure 

 5 {L.L.Asc.,Des.,a and b). Figure 38 shows the ascending tracts, 

 and figure 41, the descending tracts in cross section, under high 

 magnification. 



2. The visceral sensory component. The proximal portion of the 

 geniculate ganglion has not changed its position noticeably (fig. 

 3, G. gen.). Distally it projects to the spiracular pouch, where 

 its appearance has materially changed. Along the caudal aspect 

 of the entodermal wall of the pouch a fiber or two may be traced 

 along the bases of the entodermal cells. Their course, however. 



