THE CEANIAL ]\'ERVES AND LATERAL SENSE ORGANS OF FISHES. 153 



nerves usually considered to be branches of the trigemiuus really belonged to the 

 facial. To Friaut, therefore, belongs the credit of being tlie first autlior to arrive 

 (approximately) at the truth with regard to the innervation of the lateral sense orgaas. 

 His work was confirmed by Marshall and Spencer in 1881 and by Mlis in 1889, and it 

 was thus established that the superficial oplithalmic and buccal lateral Hue nerves 

 belonged to the facial, rather than to the trigeminal, nerve. The work of Beard and 

 Froriep in 1885, imjiortant as it is, has added considerably to the confusion wiiich 

 exists on the subject. There can be no doubt that if the branchial or epibranchial 

 sense organs ultimately develop into the lateral sense organs of the adult, then the 

 latter must have been (primitively) segmental structui'es. But we have seen there is 

 good evidence against the iilentity of the two series of sense organs, and even before 

 this evidence transpired it is significant that the innervation of the adult lateral sense- 

 organs could not be harmonised with the supposed embryonic conditions (cp. especially 

 Allis and Ewart). And added to this the fact that the lateral organs and the auditory 

 organ have been found to develop from a common sensory anlage, which discovery has 

 been extended to several forms and has been found to apply to Elasmobraiiclis as well as 

 to specialised Teleosts, we have an opposing view of the development of the lateral 

 organs which has the advantage of being easily reconcilable with the facts of adult 

 structure. This leads us to the latter view of the question. 



In his 1889 paper, Allis, independently following Friant, and working on the lines laid 

 down by Marshall and Spencer, described the lateral line nerves as branches of the facial, 

 glossopharyngeal, and vagus nerves. In this he was largely followed by Ewart (1892) 

 and Pinkus (1894)), until it was considered completely established that the lateral nerves 

 were undoubtedly branches of the facial and vagus, and perhaps also of the glosso- 

 pliaryngeus. In the meantime Mayser (1882), Pollard (1892), and Strong (1895) had 

 been working out a totally different hypothesis, the tendency of which was in the first 

 place to regard all the lateral line nerves as morphologically branches of one trunk, and 

 in the second to associate that trunk with the auditory irerve and system. This view 

 was developed by me in my Cliimcera paper, in which I endeavoured to show that the 

 lateral line system was an independent system of sense organs innervated by a distinctive 

 and independent series of nerves of characteristic size of fibre, and further that the 

 whole was the morphological equivalent of the auditory organ, with which it should 

 therefore be associated. I further stated the belief that the branch of the glosso- 

 pharyngeus innervating sense organs of the lateral line would be found on investigation 

 to be a branch of one of the lateral line nerves, and finally, pending further investigation, 

 provisionally associated the lateral line nerves with the facialis. These views have been 

 entirely confirmed by recent investigations, such as tliose in 1897 by Kingsbury, Herrick, 

 and Allis, so that the j)i"esent position, from the point of view of the comparative 

 anatomist, and setting aside for the moment purely developmental evidence, may bo 

 summarised as follows : — 



(1) The lateral line system is an indejoendent series of sense organs, differing histo- 

 logically from any other cutaneous sensory system, such as the terminal buds described 

 by Merkel and other authors, and not innervated by the same nerves. 



