METAMERISM. 255 



of its composition in the lower fishes. If this proves to 

 be the case, it is clear that in the higher fishes it contains, 

 for the reasons already mentioned, only the two visceral 

 components. 



The lateral line branches of the cranial nerves have 

 usually been considered equivalent to the lateral or medial 

 rami of the spinal nerves. Thus, the r. lateralis vagi 

 has often been described as a "collector" of these medial 

 rami, and very recently both Furbringer ('97) and Neal 

 ('98, p. 271 and p. 211) consider that these medial rami 

 have been "supplanted" by the r. lateralis vagi. To this 

 there are at least two very grave objections. In the first 

 place, these medial rami have not been supplanted at all 

 in the bony fishes but they, and they alone, innervate all of 

 the skin and all of the muscles of the dorso-lateral regions 

 of the body. Neither the r. lateralis X nor the r. lateralis 

 accessorius participate in the innervation of these cutane- 

 ous areas, but supply only special sense organs which 

 have migrated in the ontogeny back from the head. And 

 from this it follows, in the second place, that these recur- 

 rent nerves would be incapable of supplanting the dorsal 

 or medial spinal branches, for they are not of equivalent 

 structure or function. This case is totally different from 

 that of the r. intestinalis, where there has been a supplant- 

 ing of visceral spinal fibres by visceral cranial fibres. 



In the same way we must avoid homologizing such dor- 

 sal cranial nerves as the r. supra-temporalis, composed of 

 lateralis fibres, with the general cutaneous fibres of the 

 dorsal rami of the spinal nerves. The rami cutanei dor- 

 sales of the vagus and the r. ophthalmicus superficialis V 

 (and possibly the general cutaneous fibres with the r. 

 oticus) are the only nerves in the head of Menidia which 

 can be homologized with dorsal spinal rami, though in 



