62 PROFESSOR J. C. EWART ON THE 



masses (groups of ampullae) which Jacobson considered sense organs, St Hilaire (1801) 

 described as electric organs (9), and this extraordinary mistake was also made by Mayer 

 (10) (1843), Jobert de Lamballe (11) (1858), and M'Donnell (12) (1861). As early as 

 1822, Blainville (13) pointed out St Hilaire's mistake; and Eobin (14) and several 

 others have confirmed the observations of Blainville, as to the correctness of which there 

 can no longer be any doubt, notwithstanding M'Donnell's statements to the contrary. 

 Unfortunately, Mr Darwin refers to M'Donnell's observations, and remarks, in the 



Ongin of Species (p. 150, 6th edition) : — "In the Ray there is an organ near 



the head, not known to be electrical, but which appears to be the real homologue of the 

 electric battery of the Torpedo." M'Donnell's homologue of the torpedo's battery, 

 which exists in sharks, as well as rays, will be afterwards described as the hyoid group 

 of ampullae. 



Trevlranus (15), who was one of the first to describe the central masses (ampullary 

 groups) in sharks, considered them as sensory structures. Savi (16), Robin, and others, 

 followed Jacobson and Treviranus ; while Della Chiaje (17), probably unacquainted 

 with Jacobson's work, like Monro, considered the mucous canals as simply concerned in 

 the secretion of mucus. 



But little real progress was made until Leydig and H. Muller directed their attention 

 to the subject. Leydig's first paper appeared in 1850 (18); but it was not until 1868 that 

 he published a full account of his observations. Leydig's monograph ( Ueber Organe eines 

 sechsten Sinnes) is by far the most important work that has hitherto been published on 

 the lateral sense organs of fishes (19). The author points out that, from the morphologist's 

 standpoint, not only the mucous canals — the sensory and ampullary canals — but also 

 the peculiar little follicles found in the torpedo by Savi, are all sensory organs. They 

 were together regarded by Leydig as the organs of a sixth sense. 



H. Muller, like Leydig, considered the follicles of Savi, as well as the two forms of 

 mucous canals (sensory and ampullary), as concerned in sensation rather than in secre- 

 tion. His observations (20) were published seventeen years before the important memoir 

 by Leydig. Kolliker (21) and Max Schultze (22), prior to 1868, had pointed out the 

 existence of sensory cells in the follicles of Savi. 



Since 1868, amongst others who have worked at the lateral sense organs of fishes, 

 may be mentioned Boll, Goette, Semper, Balfour, Sappey, Beard, Garman, Allis, and 

 Fritsch. Boll (23) refers especially to the structure of the ampullae and their canals. 

 Goette (24), Semper (25), Balfour (26), and Beard's (27) work relates chiefly to the 

 development of the canals and their nerves ; while Sappey's (28) work is, in a manner, 

 an extension of the investigations of Monro. Garman (29), who studied the canals 

 chiefly with a view to ascertaining their value in classification, shortly describes and 

 figures their arrangement in a large number of sharks and rays ; while Allis (30) gives 

 an able and exhaustive account of the lateral line system in Amia. Fritsch (31 and 32) 

 deals with the canal system in the Selachia as a whole, and also describes shortly the 

 lateral sense organs of the torpedo, and peculiar little follicles (syalt-papillen) which he 



