188 JOHN BEARD. 



of the posterior elements of the vagus, and, as stated before, vg. 2, 3, 

 and 4, all give fibres to the lateral line. 



It is worth mentioning here, because these researches confirm one 

 of Balfour's views, that the "lateral line" was originally, as he 

 believed, restricted to the anterior part of the body. The whole 

 development of all these branchial sense organs shows the truth of 

 this. But it is, at the same time, a very curious fact that these sense 

 organs along the trunk of Teleostei are segmental (fig. 44, br.o.). 

 This is well known, and is figured in the above figure, which is part 

 of a horizontal section of a salmon hatched about six weeks. 



At one time I believed, with Eisig and others, that great morpho- 

 logical importance could be attached to these facts ; but I feel now 

 compelled to adopt Balfour's view, and in discussing the morphology 

 of these sense organs I shall strongly urge that in face of the facts of 

 development here recorded, the morphological connection between 

 these branchial sense organs of Vertebrates and the " Seitenorgane " 

 of Capitellidse, first suggested by Eisig, 1 becomes of a very doubtful 

 nature. And here again I may be permitted to remind the reader 

 that Balfour 2 long ago rejected the existence of any homology between 

 these two sets of organs. 



Vagus in Amphibia. 



Mr. Spencer has recorded in this Journal 3 certain observations on 

 the nerves of Amphibians. He has found that not merely the ganglia 

 of the dorsal roots of cranial nerves of Amphibians, but that the whole 

 of the nerves themselves are split off from the skin. I have figured 

 the origin of the vagus nerve and ganglion in the frog in fig. 27. I 

 have investigated the facts in Amphibians, and can fully confirm Mr. 

 Spencer in most points. The development as seen in Amphibians is 

 interesting, as in some respects showing a very primitive condition of 

 the nervous system, viz. a nerve sheath or part of one ; in other 

 respects it is impossible in them to get as good a view of the primitive 

 nerve composition of the head as in Elasmobranchs. 



In Amphibians a considerable amount of fusion of once separate 

 nerves has taken place, not only behind the auditory organ, but also 

 in front of it. As an instance, it may be mentioned that the ciliary 



1 Eisig, "Die Seitenorgane der Capitelliden," 'Mittheil. a. d. Zool. Stat. z. Neapel,' 

 vol. i., 142. 



2 Balfour, 'Comp. Embryol.,' vol. ii., p. 142. 



3 ' Quart. Journ. Micr. Sc.,' Supplement, July 1885. 



