880 



PACINIAN BODIES. 



tice. % The prisms of the electrical organ, as 

 Hunter described, are divided by very nume- 

 rous horizontal diaphragms into spaces con- 

 taining a thin fluid, and on these diaphragms 

 the nerves and vessels of the organ are ulti- 

 mately distributed in great abundance. Each 

 of these superposed diaphragms consists of a 

 layer, possibly double, in and not upon which 

 the nerves ramify. The nerves of the electrical 

 organ have never any ganglia formed upon 

 them. Their tubules always have the double 

 contour which marks the presence of the white 

 substance of Schwann. The ramifications pe- 

 netrate between the prisms, and each diaphragm 

 receives tubular fibres at several points of its 

 circumference, though Savi is doubtful whether 

 these are derived from two or more tubules of 

 the branch supplying them. In the diaphragm, 

 however, they are uniformly spread out in a 

 network with five or six-sided meshes, the 

 sides of which are everywhere formed by a 

 single tubule with double contour of the same 

 diameter and structure as the tubules of the 

 trunk of the nerve. If this network is supplied 

 from several different tubules, these tubules 

 must be described as inosculating to form it; 

 if from a single tubule, this must be regarded 

 as again and again branching dichotomously, 

 and the branches repeatedly anastomosing. 

 Whichever be correct, the existence of a true 

 network of ultimate nerve-tubes with double 

 contour is certainly a fact of much importance, 

 and hitherto unique ; and it appears to be 

 satisfactorily established by the repeated accu- 

 rate observations of Savi. 



The series of superposed membranes in the 

 prisms of the electrical organs may have an 

 analogy with the concentric capsules of the 

 Pacinian bodies. Their separation by inter- 

 vening fluid is another point of resemblance. 

 But in their relation to the nerves they are 

 quite unlike. In the one, each membrane has 

 a plane network of nervous tubules in its sub- 

 stance ; in the other a single nerve-fibre is 

 placed in the axis of a series of concentric 

 membranes. The condition of the nerves is 

 also different. In the one the white substance 

 of Schwann everywhere invests the nerve ; in 

 the other it is suddenly lost on entering the 

 central capsule. The branching of the nerve- 

 tubes in the electrical organ has a correspon- 

 dence with the frequent tendency of the pale 

 fibre of the Pacinian corpuscle to divide into 

 two or more parts. On the whole, perhaps, 

 the comparison may suffice to raise the ques- 

 tion, whether the Pacinian corpuscles may not 

 be organs designed to generate some kind of 

 force, which the nervous communication with 

 the centres may serve to connect either with 

 volition or some emotional impulse or feeling.* 



There is another set of organs, however, in 

 the electric torpedo, the discovery of which we 

 owe to Savi, and which bear a closer resem- 

 blance to the Pacinian corpuscles than the 

 electric organs themselves. These are what he 

 terms the J'ollicular nervous apparatus, and 



* Henle and Kblliker endeavoured to elicit evi- 

 df.nco of an electric discharge from the Pacinian 

 bodies of the cat's abdomen, but without success. 



which I shall briefly describe nearly in his own 

 words.* 



" This apparatus is found bordering the an- 

 terior part of the mouth and nostrils, and ex- 

 tends over the surface of the anterior part of the 

 electrical organs, and over the front half of 

 their outer edge, where it rests upon the carti- 

 lage and aponeurotic coverings of the fin. 

 Some parts of the apparatus are found on the 

 back, but the greater portion on the ventral 

 surface of the animal. It consists of extensive 

 linear series of follicles, or closed membranous 

 cells with double walls filled with a gelatinous 

 fluid, and enclosing a small amorphous granular 

 mass, which nearly resembles the amorphous 

 grey matter of the cerebral hemispheres. A 

 nervous branch gives some fibres to this granu- 

 lar mass, while other similar fibres united into 

 bundles pass out of the follicle, penetrate the 

 grey mass of the adjoining follicle, and mingle 

 with its nerve. 



" The nerves distributed to this apparatus 

 come exclusively from the fifth pair, and more 

 particularly from the branchesspringing from the 

 anterior portion of the root. Each follicle (fig. 

 486) is of a spheroidal form, slightly compressed 

 on the side which adheres to the neighbouring fol- 

 licle, and its diameter is about -^th of an inch. I 

 have found these dimensions the same in ani- 

 mals of very different size. These follicles are 

 never free or floating in the gelatinous fluid so 

 abundant in these fishes : on the contrary, they 

 are always firmly fixed, as if with a special view 

 to their security, for they are planted on un- 

 yielding aponeurotic expansions, like that of 

 the muzzle, or else on fibrous bands extending 

 along the fin, and having no other use. When 

 the gelatinous fluid which envelopes these folli- 

 cles is examined under the microscope, it is 

 seen to contain numerous fibres passing in va- 

 rious directions, and fixed to the surface of the 

 follicles. 



" Each follicle is formed of two membranes 

 (f and g) which adhere together on the side 

 towards the fibrous band which supports the 

 organ, whilst on the opposite side they are 

 separated by about a third of the vertical 

 diameter of the follicle. These organs mny be 

 easily examined by a very slight magnifying; 

 power, it being only necessary in the first place 

 to remove the investing gelatinous substance, 

 and then to subject them to moderate compres- 

 sion for the display of their interior. In a 

 follicle thus compressed, we observe first the 

 cut portion of the tendinous band cc, then the 

 outer membrane enclosing the other, in which 

 is the rounded granular mass e already men- 

 tioned. This latter seems to rest upon the 

 lower wall of the internal membrane. The ex- 

 ternal membrane adheres by its lower border to 

 the fibrous band beneath it in such a way, that 

 between this external wall of the follicle and 

 the internal is left a space, in which the nervous 

 ramification d advances and adheres to the 

 rounded mass of granular substance. 



" In the follic'es of the longitudinal series 

 of the fin, of which we here speak, the nervous 



* Op. cit. p. 332. 



