THE CRANIAL NEEVES AND LATERAL SENSE ORGANS OF EiSilES. 195 



Acusticuswurzel," and regards the semicircular canals as modified lateral tubes. I 

 entirely concur with Ayei-s that " Mayser was mucli nearer the truth tlian he ever 

 realised when he arrived at the conclusion above quoted " (7, p. 112). Mayscr's discovery 

 of the common origin of the two sets of fibres has been fully confirmed and also extended 

 by many subsequent authors, such as Strong, Kingsbury, and Herrick, so that it 

 must now be considered as an established fact. Bodenstein (1882, 24) briefly discusses 

 (p. 137) Mayser's conclusions, and largely concurs. He compares the semicircular canals 

 with the canals of the lateral line, and considers the endolymph of the ear to correspond 

 to the mucus in the lateral canals, but is somewhat inconsistent in regarding the 

 auditory organ as phylogenetically older than the lateral line system. 



Beard (1884, 17) looked at the question irom a new aspect when, instead of regarding 

 the lateral system as an accessory auditory organ, and therefore discounting the value 

 of the comparison by im2:)lying that tlie two systems are only homoplastic and not 

 homologous structures, he derived the auditory organ from the lateral line system, and 

 concludes that '• the auditory organ of Vertebrates is fundamentally a specialised portion 

 of the system of sense organs of the lateral line." This view, that the ancestral Verte- 

 brate possessed a system of lateral sense organs which gave ri'^e lioth to the auditory organ 

 and to the modern lateral line system, has been abundantly supported by further 

 evidence, and now stands as one of the most probable views of vertebrate cephalogenesis. 

 Beard subsequently developed his hypothesis (1885, 19), and considered, with Gegeubaur, 

 Marshall, Balfour, and other embryologists, that the auditory nerve was a dorsal branch 

 of the facial. 



In 1884, Wright (227) followed Bodenstein in comparing the endolymph of the ear 

 with the mucus in the lateral canals, and in a further publication in the same year (228) 

 independently confirms Mayser by describing a common origin in the brain for the 

 lateral line and auditory nerves of Amiurus. He, however, still perpetuated the mistake 

 of his predecessors in classing most of the lateral line nerves with the trigeminus, and 

 further states, what m.ust be regarded as doubtful, that the buccal nerve " contains fibres 

 other than those derived from the tuberculiim aciisticmn." Eisig (1887, 65) discusses 

 Beard's derivation of the auditory organ from lateral sense organs, and is favourably 

 disposed towards the view (pp. 711-712) ; whilst Fritsch (1887, 75), who was unable to 

 find a cupula to the lateral sense organs of Ilalaptenii-us, advances the extraordinary 

 explanation that it may have been washed away by the passage of sea water through the 

 canals. 



The cousins Sarasin (1887, 177), who favour the derivation of the auditory organ from 

 lateral sense organs, and further consider that the latter function as accessory auditory 

 organs, enter into an elaborate comparison between the histology of the auditory and 

 lateral sense organs, and endeavour to establish that both are identical in all essential 

 respects. Cunningham (1890, 55), discussing the cupula of the lateral sense organs, is 

 " inclined to think the cupula is, during life, of a mucous nature, and therefore semi-liquid. 

 It seems certain that the sensory hairs are imbedded in the cupula. It is difficult to 

 understand how such cells as those of the sense organ should secrete mucus or form a 

 cuticle ; perhaps the cupula is nothing more than the ordinary mucus of the dermal tube, 



SECOND StUlIES. — ZOOLOGY, VOL. VII. 27 



