DIFFERENTIATIONS OF ECTODERM IN NECTURUS. 499 
of fibres belonging to this group enters the intersegmental 
ridge on the posterior margin of the third vagus cleft. This is 
the beginning of the nerve of the ventral lateral line of the 
trunk. 
There is a small nerve connecting the glossopharyngeal 
ganglion with the branchial sense-organ below the ear, which 
is not represented in the drawing. 
Fibres of the ramus ophthalmicus superficialis facialis have 
just left the skin at the posterior limit of the supra-orbital 
ridge, while the ramus buccalis begins to be formed at the 
dorsal extremity of the infra-orbital ridge. A small branch not 
represented in the drawing connects the primitive sense-organ 
above the hyomandibular cleft with the facial ganglion, while a 
prolongation of the facial ganglion fuses with the dorsal margin 
of the hyomandibular ridge, although I find as yet no nerve- 
fibres here. 
3. Comparative and Critical. 
v. Wijhe (87) first called attention to the fact that the cells 
of the neural crest in the Selachii fuse with the ectoderm in 
two planes. Misses Johnson and Sheldon (21), in their “‘ Notes 
on the Development of the Newt,” extend this observation to 
the Amphibia, The first fusion occurs, they tell us, “ above 
the level of the notochord ;” and in the cases of facial and 
glossopharyngeal ganglia a second fusion takes place “ in the 
dorsal wall of the corresponding gill cleft.”” Like v. Wijhe, 
they find the dorsal fusion connected with the development of 
the lateral Jine. 
Froriep (138) believes the ventral fusion found in the Selachii 
to be the homologue of a similar union of ectoderm and 
ganglion which he discovered in the Mammalia, and first 
associated with the gill clefts as ‘‘ Kiemenpaltenorgan.” 
v. Kupffer (22, 23) shows that the neural Anlagen in 
Petromyzon also fuse with the skin in both dorsal (lateral) 
and ventral (epibranchial) lines, receiving at each place of 
fusion large ganglionic additions from the ectoderm. These 
fusions between ectoderm and ganglion, which v. Kupffer finds 
