THE SENSORY CANAL SYSTEM OF FISHES, 501 
species of skate, and in 1669 of a similar system in one of the 
sharks. Lorenzini (50) in 1678 confirmed the observations of 
Stenonis and separated the canals into two systems, viz. sensory 
and ampullary canals. Monro secundus (56) in 1785 investi- 
gated and figured the canals in the head of a cod and a skate ; 
he further traced the innervation of the ampullary canals. 
Seeing that Monro regarded the system as one for the secretion 
of mucus, it seems probable that he was not acquainted with 
Lorenzini’s work. Geoffrey St. Hilaire (34), 1802, regarded 
the mucous ducts as the analogues of the electric organs of the 
torpedo. Jacobson (88), 1813, was the first to put forward a 
theory that this system of canals were sensory organs for the 
transmission of vibrations of the water to the nerves. His 
theory was more or less supported by Treviranus, Knox, and 
others. Mayer, 1843, Jobert de Lamballe (40), 1858, and 
M‘Donnell (51), 1861, all regarded them as electric organs ; 
while Blainville, 1822, Savi, 1840, and Robin (64) held that 
they were mucous canals. 
Wagner, 1847, H. Miiller, 1851, Kolliker, 1856-8, Max 
Schultz, 1862, Boll (10), 1868, and many other anatomists 
gave considerable attention to the subject, but little advance 
was made until 1868, when Leydig (48) published his com- 
prehensive paper. Commencing in 1850, his series of papers 
form by far the most complete and important contribution to 
the subject that has yet been published. 
More recent contributions on the development, innervation, 
and histology have been advanced by Gotte, Semper, Balfour 
(8 and 4), Solger (72, &c.), Hisig (28), Dercum (21), van 
Wijhe (82 and 83), Hoffmann (35), Wright (84), Fritsch (28 
and 29), Sappey (67), Beard (7), and others. 
De Sede (22) in 1884 published an interesting paper detail- 
ing his results upon the function. He was the first to compare 
the system with a view to ascertaining its value in classification, 
and in the Selachia accords to them greater importance for 
such purposes than in the Teleostei. Garman (82) in 1888, in 
an exceedingly valuable paper, described and figured the 
course of the canals in a large series of Selachia and Holo- 
