FISHES. 375 



pleuronectes, but to many others which appear to yield to none in the 

 rapidity and facility of their movements, as the mackarel, for example. 

 The presence or absence of the natatory bladder is not even consistent 

 with the other relations of conformation of fishes, and even in the 

 mackarel genus, a species very similar to the common mackarel, 

 (the scomb. pneumatojjhorus of Laroch.), is found provided with it*. 

 There are many similar examples ; the polynemu? ])aradisa?us wants 

 it, whilst all the rest of the genus are provided with it; it is very large 

 in the sebastes, and in a neighbouring genus, the pelores (m), it is 

 scarcely the size of a pea. 



The power with which a small number of fishes is endowed of 

 producing electric shocks, may also be ranked amongst their greatest 

 singularities of organization, so much the more as the organs by 

 which they exercise this power do not differ less between themselves 

 than they differ from organs of other kinds. 



In the torpedo, there are membranous tubes filled with mucus, and 

 divided by transverse septa, which are closely compacted together, 

 like the radii of bees, in two groups placed on each side of the head, 

 and which receive enormous branches from the fifth and eighth 

 pairs of nervesf. In the gymnotus, we find this apparatus occupying 

 the whole under part of its body to an immense thickness, formed 

 by parallel laminee, which are separated by very delicate layers of 

 mucilage J. 



In the silures, two layers, of different substances, are interposed 

 between the skin and muscles throughout the greater part of the body. 

 The external one is cellular, and its external surface aponeurotic ; it 

 receives the nerves of the fifth pair. The internal layer is of a floccu- 

 lent tissue ; and derives its nerves from the intercostals §. 



* See the Memoire of M. de Laroche, upon the anatomy of the natatory bladder 

 of fishes, and my report upon this Memoire, in the Annales du Museum, t. XVI. 



f The benumbing power of the torpedo was well known to the ancients, and both 

 Ossian and Claudian have celebrated it in song. Among the moderns, Borelli and 

 Redi have been occupied with it. Lorenzini, in 1678, in a special work Ohserva- 

 soni intorno aUe torpidini ; Koempber, in 1712, Amon. exot., p. 509 ; Reaumur, in 

 1714, Mem. de I'Acad. des Sciences, p. 344, have described this singular action, 

 and the organs which were the seat of it. The latter were dissected and examined 

 more in detail by J. Hunter, Phil. Trans. 1773, vol. 63. The electric nature of the 

 shock was determined by Walsh's experiments in 1772, at the island of R^, and 

 Rochelle, and his account reported in the same volume of the Transactions, as also 

 in vol. IV of the Journ. de Physics. The organs have likewise been described by 

 M. Geoflfroy, Ann. du Mus. vol. 1 ; but he has very unwittingly believed them to be 

 representatives of the mucous vessels of the rays. The latter vessels are found in 

 the torpedo quite independently of the electric organs. 



X The electric power of the gymnotus, has been discovered by Richter, Mem. de 

 I'Acad., 1677; and described by Lacondamene, Brankroft, and Fermin. Its nature 

 has been recognized since 1757, by Sgravesand, Governor of Essequibo, according 

 to what AUamand points out. In 1755, Walsh completed the demonstration by 

 obtaining sparks. The organ has been described by J. Hunter, in vol. 65 of the 

 Philos. Trans. 



§ It was Adanson who made known, in 1751, the benumbing power of the 

 Silurus, and described it as resembling, in its effects, those of the l^f ydon jar ; this 

 is the first example discovered of the analogy subsisting between this sort of pheno- 

 menon and electricity. The electric organ of the silurus, has been described by M. 

 Geoffroy, Ann. du Mus. vol. 1 , p. 3, pi. 26, f. 4 ; and with more exactness by M. 

 Rudolphi, Mem. de I'Acad. of Berlin, 1824, p. 137, et seq. and pi. l to 4. 



