THE LATERAL SENSE ORGANS OF ELASMOBRANCHS. 471 



account given by Cuvier and Valenciennes in their Natural History of Fishes. 

 Dealing with the " Electric Organs of Electric Fishes," he describes a single pair of 

 ampullary capsules in the skate, and, reverting to the standpoint of St Hilaire, 

 concludes that these represent an elementary electric apparatus comparable to that 

 of Torpedo. 



Eckhard, dealing with Torpedo alone, went into the microscopic structure of the 

 ampullae in considerable detail, and concluded that the six spheres contained in each 

 ampulla are peripheral ganglia. While considering it as proved that these organs 

 are not secretory, he was non-committal as to what type of sensory function they 

 might fulfil. 



M'Donnell (1861) rejected St Hilaire's theory, and supported Leydig's view of 

 the tactile function of the muciferous tube system of sharks and rays. 



Boll (1868), m his work on Lorenzini's ampullae in Torpedo and an unnamed 

 species of shark, devoted much attention to their histology, and confirmed Leydig's 

 view as to their partitioned structure. 



The researches of Todaro (1870) are referred to by both Merkel and Fritsch, 

 who followed him, but his " Contribuzione " have unfortunately not been available 

 for reference. 



Balfour (1878), who was the first to deal with the subject from the embryological 

 point of view, pronounced in his work on The Development of Elasmobranch Fishes 

 that the ampullary canals are products of the mucous layer of the epiblast. 



The work of Sappey (1879) contains more detail as to the distribution of the 

 canals than that of any of his predecessors. He gives detailed accounts of the 

 grouping of them in a skate (la raie) of which he does not give the specific name, 

 but the description as far as it goes is applicable to several of the genus, although 

 it is incomplete in giving an account of only three pairs of capsules. He repudiated 

 Leydig's view as to the sensory function of these organs, and maintained the glandular 

 structure of both the ampullae and their ducts, the function of which, he considered, 

 was to pour mucus on the surface of the skin, although he admitted the use of the 

 mucus to be still in doubt. 



Merkel's researches (1880) dealt with the nerve-endings and sensory cells of the 

 system in Elasmobranchs generally, of which he investigated a number of different 

 species. After a detailed study of the histology of the ampullae, he arrived at the 

 conclusion, confirming that of Jacobson and his followers, that the sensory function 

 of these organs is established beyond all question, and that the probability of this 

 function being of a tactile nature has much to support it. 



Ten years later we find again in the work of Fritsch (1890) a reversion to the 

 theory of secretion. In the section of his memoir on Electric Fishes dealing with 

 Torpedoes he expressed the opinion that the ampullary canal system is a part of the 

 lateral canal system, from which it has become separated in structure and in function, 

 and that thus, while the lateral canal system is sensory in function, the ampullary 



