DIFFERENTIATIONS OF ECTODERM IN NECTURUS. 505 
covering the same segments. The root of the buccalis derives 
its fibres from a more ventral band of sensory tissue on these 
very segments. The otic branch of the facialis contains fibres 
arising originally from the median part of the anterior of the 
two intersegmental ridges meeting in the hyomandibular cleft. 
The sensory fibres in the hyomandibular root of the facialis 
come from the ventral portions of the two intersegmental 
ridges here united. The following primitive intersegmental 
line of sensory epithelium supplies from its dorsal region 
branches to the root of the auditory nerve, from its median 
region fibres to the so-called ‘dorsal root” of the glosso- 
pharyngeus ; and from the incomplete account of the innerva- 
tion of sense-organs on the gular plate given by Allis (1) in 
his description of the lateral line in Amia, we must conclude 
that the ventral portion of the intersegmental ridge at the 
margin of either the hyobranchial or first branchial cleft is 
also represented in the ‘‘ root” of the glossopharyngeal nerve. 
A band of tissue on the successive vagus segments sends its 
fibres to the “root” of the lateral line nerve in the glosso- 
pharyngeal segment, but also sends fibres to the ‘‘ roots” of 
the vagus nerve. I will go no further than to add that, as far 
as the lateral line organs are concerned, their fibres choose the 
nearest and most direct path to the auditory centres in the 
brain, which seem to be also the centres of the entire lateral 
line system, yet both development and comparative anatomy 
tend to show that it is a matter of little moment whether these 
fibres enter the brain by one nerve-root or another. 
4. The Development of the Spinal Nerves, and the 
Relation of the Vagus Ganglion to its Myotome. 
In Pl. 38, fig. 1, I have indicated the position of the anterior 
spinal ganglia. There is in Necturus one ganglion for each 
segment of the head and trunk, if one regards the auditory- 
facial group as composed of two primitive ganglia. As I have 
already mentioned, the preemandibular segment is not distinct 
from the mandibular which contains the Gasserian ganglion. 
To the following two segments would belong the auditory- 
