DIFFERENTIATIONS OF ECTODERM IN NECTURUS. o01 
or again, as on the path of the lateral line of the trunk, cells 
may migrate individually from the sensory ridge into the 
ganglion; but just that relation of ganglion and sense-organ 
which Beard describes I have never found in Necturus. 
In designating the several divisions of the lateral line system 
I shall adopt the plan of Ewart (10) rather than that of Allis 
(1), as I also think it wise to associate each division of the 
system with the particular nerve it supplies. The infra-orbital 
line is thus limited to that part of the system which gives rise 
to the ramus buccalis. For the organs that develop from the 
sensory epithelium above the hyomandibular cleft Ewart 
suggests the appellation “otic,” and “ glossopharyngeal” or 
“temporal ” for those developing from the primitive sensory 
epithelium in connection with the glossopharyngeal nerve. 
The line of organs formed from the longitudinal ridge 
external to the vagus ganglion I shall call the epibranchial 
line, as they give rise to an independent nerve in Necturus, 
and do not form part of one of the sensory lines of the trunk. 
I must take exception, however, to Ewart’s statement that, 
from the contact of the buccal and superficial ophthalmic 
ganglia at their proximal ends, “‘it might be inferred that 
there has been a splitting of the original epidermic thickening 
above the spiracular cleft, the splitting resulting not only in 
the formation of two ganglia, but also of two sensory canals— 
the supra-orbital above and the infra-orbital below the eyeball.” 
The development of these lines in Necturus does not support 
this view. The supra-orbital line of sense-organs traces its 
origin to the anterior part of the primitive dorso-lateral ridge, 
which developed in approximately its present length when the 
cells of the neural crest were still connected with the mid- 
dorsal wall of the brain, at a period consequently long preceding 
that in which the proper lateral line system begins. The cells 
of the ramus ophthalmicus profundus trigemini are connected 
with the anterior part of the primitive ridge at the time 
when the posterior part of the ridge begins to assume a radial 
structure, and to give rise to fibres of the ramus ophthalmicus 
superficialis facialis, 
