194 MR. F. J. COLE ON THE STEUCTUKE AND MOKPHOLOGT OF 



instead of an ampuUary tube, and every condition for the development of a canal would be 

 satisfied, since the latter, as we know, is formed in segments. This brings us to the final 

 question as to whether the canals were originally formed as continuous furrows or by the 

 fusion of contio-uous pieces. On this point the evidence is unanimous and conclusive. 

 The comparative anatomy of the different classes of sense organs and canals, and 

 especially the development of tlie latter where known, prove beyond doubt that the 

 lateral canals were formed, not by the closure of continuous furrows, but by the fusion 

 end to end of adjacent tubes. The precise processes, as far as can be judged, would take 

 place in the following order : — (1) Formation of cords of indifferent cells along the lines 

 of the future canals ; (2) differentiation of sense organs along these cords ; (3) sinking 

 down of each sense organ to form a furrow, and the fusion of the lips of the furrow to form 

 a tube open at each end ; (4) fusion end to end of series of these tubes in such a way that 

 continuous canals are formed, and there is an opening on to the surface between each 

 two sense organs. Such, I believe, has been the phylogeny of the sensory canals, and 

 the question must now be left for further investigation either to substantiate or to 

 disprove this view. 



S. The Lateral Sense Organs and the Auditory Organ. 



Thomas Willis (1664, 224) may be said to have suggested the morphology of the 

 auditory organ to his better informed successors, when, in the same year that the 

 lateral line system was discovered, he described the auditory nerve as the dorsal branch 

 of the VIIth,and considered both nerves to constitute the seventh pair of cerebral nerves. 

 Leydig, however, was the first to derive the auditory organ from lateral sense organs 

 (1850, 120), but he unhappily recanted in 186S (126), and described the lateral 

 oro'ans as forming an organ of 6th sense, and having no morphological connection 

 with the auditory organ. In 1870 (182) Schulze, who erroneously thought that water 

 flowed through the sensory canals, regarded the latter as accessory auditory organs ; 

 whilst Dercum (1880, 59) went still further, and minutely compared the histology of the 

 lateral sense organs with the maculae of the ear, concluding that they resembled each 

 other in every essential respect. Emery (1880, 66), who agrees with Schulze that the 

 lateral organs represent an accessory auditory system, first discovered that the lateral 

 oro-ans possess a well marked cupula, which he believed to be foi'med of successive 

 cuticles secreted by the peripheral cells of the sense organ, and correctly compared with the 

 cupula terminalis of the ear. This important and interesting discovery has been extended 

 to several other forms besides Fiei^asfer, and I find a very well marked cupula in young 

 Gadus virens (see PL 23. fig. 4). 



The important work by Mayser (1882, 135) is perhaps the first scientific contribution 

 to the question, and formed the basis upon which all further work was conducted. This 

 author discovered in Cyprinus that the fibres of the lateral line nerves and also the fibres 

 of tlie auditory nerve arose from a common centre in the brain — the tuberculum 

 acusticum. He was consequently led to regard the lateral line system as a low form of 

 auditory organ, and indted describes the lateralis lateral line nerve as the " hintere 



