1893.] 



The Electric Organ of the Skate. 



389 



which extend along the greater length of the spinal cord, one at each 

 side of the central canal. In the case of the Skate the question at 

 the outset is, granting the existence of an electric centre, is it, as in 

 Torpedo, situated in the brain or,- as in Gymnotus, in the spinal cord ? 

 Sanderson and Gotch* made out that in the Skate "a reflex centre 

 is situated in the optic lobes," but, notwithstanding this, these lobes 

 in the Skate in no way differ histologically from the corresponding 

 structures in Acanthias and other Selachians unprovided with elec- 

 trical organs. 



The development of the Skate's organ from portions of the caudal 

 my o comes, and its innervation by afferent fibres from certain caudal 

 nerve, point to the electric centre being situated in the spinal cord 

 rather than in the brain, and to its being, as in Gymnotus, on a level, 

 and all but co-extensive, with the electric organ. 



Having observed, when working at the development of the electric 

 organ, a number of large nerve-cells in the caudal portion of the 

 spinal cord, the sections of Skate embryos made some years ago 

 were first examined. It soon became evident that in sections from 

 the middle of the tail on a level with the electric organ certain cells of 

 the anterior horn of the cord were very much larger than in sections 

 through the root of the tail, and further that in late embryos and very 

 young Skate there was an electric centre, resembling in many respects 

 the electric centre in Gymnotus. 



It did not, of course, follow that "the electric nerve-cells persisted 

 into adult life. They might degenerate, and thus the supposed 

 feebleness of the Skate's organ migat be accounted for. The fact 

 that the Skate's organ increases in size as the fish grows larger led 

 me, however, to expect that large nerve-cells would be found in the 

 caudal region of the spinal cord in well-grown fish. In this I was 

 not disappointed, for, though there was ar. first some difficulty in 

 demonstrating the presence of electric nerve-cells in large fish, on ob- 

 taining perfectly fresh material their position, size, and relations were 

 easily made out, and the remarkable difference in the appearance of 

 sections of the cord at, and in front of, the root of the tail, from sec- 

 tions on a level with the electric organ, was at once evident. From 

 the observations already made, it appears that the electric centre in 

 the Skate closely resembles, from a morphological point of view at 

 least, the electric centre in Gymnotus. The electric tract is, how- 

 ever, much shorter in the Skate than in the Electric Eel, and the 

 cells are relatively fewer in number. On the other hand, the cells in 

 the Skate are larger than in Gymnotus, and this is true not only of 

 Raia batis but also of R. radiata, in which the organ is extremely 

 small and poorly developed. Nerve-cells from the electric centres of 

 Torpedo, Gymnotus, and Raia are represented in the accompanying 

 * " Journal of Physiology,' vol. 10, N 4. 



