M. Robin on a peculiar Organ found in the Rays. 23 



tions however would require to be verified upon animals fresh 

 captured. ] 



The elementary tubes which spread out against the prism are 

 from 0"^-01 to 0-013, that is to say, half the diameter of the ele- 

 mentary tubes measured on the nerves at the point of their pe- 

 netration into the apparatus. The elementary nervous tubes do 

 not terminate in a net-work, but actually in very large meshes, 

 to effect which they fork out several times into two or three 

 branches and anastomose by inosculation. 



These facts rest on the clearest evidence, being easily proved 

 even with a magnifying power of 100 diameters. The semifluid 

 nervous substance contained in these elementary tubes may be 

 made to flow out, and be seen to penetrate into each of their sub- 

 divisions and anastomoses. These anastomotic terminations of 

 the elementary nervous tubes have already been proved to exist 

 by Savi, in his " Anatomical Investigation of the Torpedo (1844)." 

 He has also proved this fact in the partitions which separate the 

 discs of gelatinous substance of the electric apparatus of this 

 fish. 



The last facts which I have just established exhibit a still 

 greater analogy between the organ in question and the apparatus 

 of the electric fishes. It is true that these nerves proceed from 

 the termination of the spinal marrow, that is to say, from the 

 Cauda equina, but the same fact takes place in the GymnotuSy the 

 most potent in its discharges of the electrical fishes, whose elec- 

 trical organs however, according to Hunter, do not receive a mass 

 of nerves proportionably so considerable as those of the Torpedo. 

 In the Ray, as in the Gymnotus, the mass of the nerves sent to 

 the electric apparatus by each nervous pair, is at least as consi- 

 derable as those which they transmit to the skin and the muscles. 

 The lateral nerve does not in the Ray, any more than in the 

 GymnotuSj send any filament to the organ in question. 



The nerves of the electrical apparatus of the Silurus, examined 

 by Geofi'roy St. Hilaire, M. Valenciennes, Rudolphi and Peters, 

 proceed from the lateral nerve, a branch of the eighth pair. 



Thus there is nothing constant in the origin of the nerves of 

 the electrical apparatus, as they proceed sometimes from the 

 eighth and ninth pair {Torpedo), sometimes from the eighth pair 

 alone {Silurus), sometimes from the pairs which arise from the 

 spinal marrow {Gymnotus and Rata). Their situation has also 

 no constancy, as they are sometimes situated towards the head 

 {Torpedo), around the body {Silurus), and on each side of the 

 tail {Gymnotus and Raia). 



The vessels of this organ are numerous and curiously arranged. 

 Between the articulation of each vertebra there passes a vessel, 

 alternately an artery and a vein, proceeding from the principal 



