90 



ANIMAL ELECTRICITY. 



strong muscles, such as are plainly designed to 

 compress them. Some of these are inserted into 

 the marginal cartilages of the fins; and there is a 

 set of very powerful ones, arranged in a cruci- 

 form manner on the ventral surface, so placed 

 as to compress the electrical organs most strongly 

 during their contraction. Dr. Davy remarks, 

 " It is only necessary to compare these muscles 

 as they exist in the torpedo with the same in 

 any other species of ray to be convinced that 

 they are adequate to, and designed for, the 

 compression of the batteries." 



Some observers, as John Hunter, state that a 

 large proportion of blood circulates through the 

 electrical organs. Girardi found the torpedo 

 much more full of blood than the other rays.* 

 But Dr. Davy says, that there are very few 

 vessels containing red blood in the organs them- 

 selves; although their tegumentary coverings 

 and the adjoining mucous system are highly 

 vascular. The arteries of the organs are 

 branches from the arteries of the gills ; their 

 veins run between the gills direct to the auricle. 

 The temperature of the electrical organs is not 

 at all higher than that of other parts of the fish. 



All anatomists who have examined the torpedo 

 have had their attention much arrested by the 

 great size of the nerves distributed to the electri- 

 cal organs. These consist of three principal 

 trunks, all arising immediately from the cerebro- 

 spinal system. The two anterior trunks are re- 

 garded by Desmoulins and Majendie f as 

 portions of the fifth pair of nerves, and the third 

 as a branch of the eighth pair. But the first 

 electrical nerve seems to have an origin altogether 

 distinct from the root of what is unquestionably 

 the main portion of the fifth pair, although it 

 certainly is in very close proximity with it, and, 

 in passing out of the cranium, the two nerves 

 seem to be in some degree united for a short 

 space. Immediately beyond this point of union, 

 the electrical nerve sends a soft twig to a small 

 cavity within the adjoining cartilage, (which Dr. 

 Davy thinks is the ear,) and then divides into 

 three small branches, and two large ones. One 

 of the small branches goes to the gills, another 

 to the neighbouring muscles, and the third to 

 the mouth. The first of the large branches runs 

 along the outer margin of the electrical organ, 

 advancing first anteriorly, then going round to 

 the posterior part of its circumference, and 

 losing itself in the mucous glands of the tegu- 

 mentary system, without sending a single twig 

 into the electrical organ itself. The other great 

 branch is inferior to the former in position, but 

 much more voluminous ; it enters the electrical 

 organ, and is ramified through its anterior third 

 part, passing between its columns, and giving 

 offnumerous twigs for the supply of the walls of 

 the columns, and the partitions, on which it 

 terminates; some of which pass even into the 

 gelatinous matter with which the columns are 

 filled. This branch, from its very origin, has 

 all its fibres separated, isolated, and parallel, 

 held together only by cellular tissue, which 

 also forms a kind of membranous sheath around 



* Mem. della Soc. Ital. iii. 553. 

 t Auut. Comp. des Systt ncrv. 



the nerve. Just as it reaches the organ, it is 

 divided horizontally into two portions, one of 

 which runs near the upper surface, the other on 

 the plane between the lower and middle thirds 

 of the thickness of the organ. 



When examined with a high magnifying 

 power, the minute branches of the electrical 

 nerves present a dotted appearance, showing as 

 if the medullary substance were arranged within 

 the sheath, not in a continuous line, but in a 

 succession of small portions with a little space 

 between each.* 



The second electrical nerve rises a little be- 

 hind the former. After leaving the cranium, it 

 divides into two large branches, which, with the 

 exception of a few twigs which go to the gills, 

 are wholly distributed in the middle third of 

 the electrical organs, in the same manner as the 

 first pair. 



The third electrical nerve arises from the brain 

 close to the second, from which, however, it is 

 separated by a thin cartilaginous plate. The 

 greater portion of it goes to the electrical organ, 

 and is distributed through its posterior third. It 

 also supplies part of the gills, the gullet, the sto- 

 mach, and the tail. Dr. Davy says it appeared 

 to him that the branch of this nerve which goes 

 to the stomach is the principal nerve of that 

 organ : it is spread over its great arch.f The 

 same observer also points out as deserving of 

 particular attention, a very large plexusof nerves 

 formed by a union of the anterior and posterior 

 cervical nerves, of the former of which there are 

 seventeen on either side, and only fourteen of 

 the latter. This plexus presents itself as a 

 single trunk just below the transverse cartilage 

 that divides the thoracic from the abdominal 

 cavity. It sends a recurrent branch to the 

 muscles and skin of the under surface of the 

 thorax; but the larger portion is distributed 

 upon the pectoral fin and the neighbouring 

 parts. The motive and sentient powers of the 

 muscles and integuments connected with the 

 electrical organs seem to depend on this 

 plexus. 



The only other peculiarity of structure in the 

 torpedo which can be supposed to be in any 

 way connected with its electrical power, is in 

 the system of mucous ducts, which is much 

 more fully developed in it than in any other ray 

 with which we are acquainted. It consists of 

 numerous groups of glands arranged chiefly 

 around the electrical organs ; and of tubes con- 

 nected with these, having strong and dense 

 coats, filled with a thick mucus secreted by the 

 glands. The tubes open chiefly on the dorsal 

 surface of the skin, and pour out the mucus, 



Dr. John Davy, Phil. Trans. 1834. 



t On this subject, Dr. Davy remarks " It is an 

 interesting fact that the nerves of the stomach are 

 derived from those supplying the electrical organs. 

 Perhaps superfluous electricity, when not required 

 for the defence of the animal, may be directed to 

 this organ to promote digestion. In the instance of 

 a fish which I had in my possession alive many days, 

 and which was frequently excited to give shocks, di- 

 gestion appeared to have been completely arrested j 

 when it died, a small fish was found in its stomach, 

 much in the same state as when it was swallowed- 

 no portion of it had been dissolved." 



