THE CEANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 1 L9 



consequently fall to tlie ground. Van Wijhe (1882, 222) was perhaps the first to draw 

 attention to the undoubted metamerism of the lateral line organs on the body in some 

 forms, and points out that each lateral line scale in Amia corresponds to a segment of 

 the body. He is inclined to think that some such relation may l)e found to exist between 

 the lateral line ossicles and the segments of the head. Beard (188 f, 17), as tlie title of 

 his paper implies, advocates the metamerism of the lateral sense organs, wdiilst Ramsay 

 Wright (1884, 227) finds that in Amiurus the sense organs of the body are n^etamerie, 

 and correspond exactly to the number of spinal nerves. 



The papers of Froriep and Beard (1885, 19) are of considerable importance, since it is 

 upon the evidence of these authors and others follf)wing them that the plea for the 

 metamerism of the lateral sense organs is very largely based. It must be pointed out at 

 the outset that the " brancliial " or " epihranchial " sense organs are only doubtfully 

 metameric, and several authors have commented on Beard's significant alteration of the 

 name from " segmental " to " branchial." The whole question depends on the metameric 

 value of the visceral clefts, but at any rate the bulk of the evidence goes to show, and 

 for the purposes of the present discussion we may admit, that if the branchial sense 

 organs are not now metameric there is strong reason for loelieving that they were so in 

 past time. The innervation of these very interesting sense-organs is, according to Beard, 

 from seven dorsal branches or supra-branchial nerves. These are : — (1) Ophthalmicus 

 profundus ; (2) superficial oijhtluvlniic of the Vth ; (3) superficial ophthalmic " of tlie 

 Vllth " ; (1) the buccal division " of the Vllth " ; (5) the dorsal or supra-temjjoral branch 

 of the IXth ; (6) the dorsal or supra-temporal ])ranch of the first division of the Xth ; 

 (7) the lateralis nerve of the remainder of the Xth. There can be no doubt that, should 

 this evidence prove trustworthy, we have very strong reasons for regarding the lateral 

 sense organs as metameric structures, since the latter are supposed to be formed by the 

 growth and extension of the branchial sense organs. 



Allis (1889, 4), without definitely committing himself to an opinion, is undoubtedly 

 favourable to the metamerism of the lateral organs, even if we only call to mind his 

 statement that they are innervated by the dorsal branches of two cranial nerves — the 

 facial and the vagus. On pp. 517-518 he destroys one of Beard's supra-branchial 

 nerves, and points out that the supra-branchial nerve from the first vagus ganglion is in 

 Amia " the first dorsal or supra-temporcil branch of the latenxl nerve,"' and hence has ni> 

 metameric significance. On p. 523, referring to Van Wij he's views above, he remarks : — 

 "The arrangement of the sense organs and nerves of the lateral system, the regular 

 occurrence of primary tubes between consecutive dermal bones of the head, as well as 

 between consecutive scales of the lateral line, and the singular correspondence between 

 the infra-orbital and opercular canals is further evidence in this same direction " 

 [*. e. of metamerism]. I am not inclined, however, to attach much weight to these 

 considerations. In the first place, there are too many exceptions to the regular occur- 

 rence of the primary pores between consecutive dermal bones for this consideration to 

 have much value *, and in the second place, although in the case of the Cod there is a 



* Allis says (p. 537) : — " Although some of the prima'')' tubes issue through the bone, one always issues between 

 every two cousecutive bones along each liuo." 



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