THE LATERAL SENSE ORGANS OF ELASMOBRANCHS. 469 



sense in sharks, tope-fishes, and rays, but he appears to have been rather a theorist 

 than an original worker. Without assigning any reason, he contradicts Treviranus's 

 statement regarding the division of the ampullae into compartments, and bases state- 

 ments of his own on microscop .al observations undertaken for him by another in 

 default of original investigations. In spite of being aware of former confusion 

 between the two canal systems, he appears himself to have fallen into the error of 

 not clearly distinguishing between them. He considers the function of the " tubular 

 organs " (ampullary canals) to be intermediate between hearing and touch, and 

 suggests that the shark's facility for tracking prey is accounted for by the possession 

 of this additional sense. 



Delle Chiaje (1839), in his work on Torpedo, shortly describes the ampullary 

 organs, introducing the subject in connection with a description of the electric 

 organ and pointing out similarities between the two systems. He mentions 

 having seen the same system with its rich nerve-supply in Zygsena, the Hammer- 

 head shark. 



The investigations of John Davy, on the electric properties of Torpedo, published 

 in 1839, were undertaken in fulfilment of a last request of his brother Sir Humphry. 

 His account includes a description of the " mucous system," the mucus of which the 

 author considers to be a good conductor of electricity, while at the same time he 

 holds that its secretion is stimulated by the electric function. No mention is made 

 of previous workers other than Lorenzini and Monro, and no distinction is drawn 

 between the sensory and ampullary canals, both of which are figured in his Plate X 

 as arising from the group of ampullae shown. 



Savi, who also worked on the electric organ of Torpedo, similarly gives an 

 account of the so-called " mucous organs." Writing in 1841, he inclines to repudiate 

 the view of the secretory function ; but in 1843 he alludes to the organs as " mucous 

 follicles," and describes their contained humour as continually flowing out on the 

 skin, although without committing himself to any theory regarding the purpose of 

 the secretion. 



Mayer, writing in the same year (1843), is said to have revived the theory that 

 the ampullae of rays are the homologue of the electric organ of Torpedo, while 

 Miescher, early in 1844, writing on "the organs discovered by Professor Mayer in 

 non-electric Rays," again reverts to the view that they are mucus-secreting structures. 

 He shortly describes for Raia clavata four pairs of these glands, evidently reckoning 

 the ophthalmic and inner buccal groups of ampullae together as one, since the other 

 three are unmistakably recognisable from the description given. 



The researches of Robin (1846) had for their object the investigation of the 

 electric organ of rays (Raia) ; and the ampullary capsules and tubes are chiefly 

 considered in order to repudiate theories suggesting their homology with the electric 

 organ. Robin limits the number of pairs of capsules in Raia to four, and claims to 

 have been the first to describe the fourth capsule (mandibular), maintaining that 



