WAYS OF THE WILD.

Auckland Star, Volume LXVIII, Issue 126, 29 May 1937, Page 1 (Supplement)

WAYS OF THE WILD.

THE ELECTRIC RAT.

DISCOVERERS OF ELECTRICITY

(By A. VT. B. POWELL.) A few weeks ago Mr. F. A. S. Moore, of Maraetai, caught a fine specimen of the electric ray and presented it to the Auckland Museum. A cast of this remarkable fish will later be exhibited. Mr. Moore caught his fish on a line off Maraetai and as toon as it was hooked he felt distinct electric shocks transmitted up the line. The electric ray averages about three feet in length and differs considerably in shape from the ordinary sting ray. The main part of the body is roughly circular and the hinder portion r&?emb«». the tail of a dogfish; quite different from the spiny whiptail and poisonbarbs of the sting ray. The power of generating electricity H not confined to this ray, for there is the so-called electric eel of the Orinoco and the Amazon, the electric catfish of the African rivers and many of the deepwater star gazers. In the electric ray, Xarcobatus fairchildi, two organs are present, lying on either side of the disc-like body, between the head and the greatly enlarged pectoral fins. Each is a large flat bodv, made up of a number of upright hexagonal tubes or columns, separated from one anotl er by walls of fibrous tissue. Each column is filled with a clear jdlylike substance and is further subdivided by thin partitions into a number of small compartments, each containing a flat electric plate. On one side of the plate is a cluster of fine nerve tendrils, which unice and join the main nerve supplying the whole organ, and this is in turn connected with t special lobe of the brain. v Transformed Muscle Fibre. The side of the plate with the nerveendings has been shown to be negative to the other side, and the current passes from the upper or positive surface of the whole organ to the lower or negative surface. In the English electric ray it has been estimated that in each of the electric organs of this fish there may be as many as 500.000 vertical columns of electric plates. It is interesting to speculate upon just how this power of generating electricity originated. If we studv the early development of the embryo of the electric ray it is found that each electric plate is nothing more than a transformed muscle fibre. Further, the whole organs have been derived from some of the branchial muscles, which have been relieved from their original duty of moving the gill-arches in order to take on this new function. As to the actual manner in which the electric current is generated very little is known, but it is fairly definite that the nervous system plays the most important part in the production of electricity. In order to obtain the full shock it is necessary to complete the circuit by touching the fish at two points, either directly or through the medium of some conducting body; it is said that a powerful sensation may be produced by a discharge conveyed through the medium of a stream of water. It is generally stated that the fish gives the shock voluntarily, the time and strength of the discharge being completely under its control. It seems more probable, however, that quite often the stimulation produced by anything touching the skin of the fish causes a similar stimulation of the nerves supplying the electric organs by ordinary reflex action. Repeated use of the organs exhausts the fish and a period of repose is necessary for recuperation. Use and Power of Shock. It seems very probable that the electric ray makes use of these electric organs to kiir or temporarily paralyse its prey. Mr. J. R. Xorman. of the Department of Zoology at the British Museum, quotes the case of two examples of electric rays taken in the estuary of the Tees, one had an eel weighing 21b and a flounder of lib in its stomach, and the other a salmon weighing nearly 51b. none of the victims showin<r any marks or blemishes on their bodies. The power of the shock seems to vary according to the number of electric plates included in the circuit, and is also dependent on the size and energy the fish. It is usually of sufficient strength to knock down a fullv grown man if he accidentally steps on one of these fish lying buried in the sand in shallow water. The electric ray was an important article of diet with the ancient Oreeks and Romans, and was regarded also as a remedy for a long list of complaints, ranging from gout to headache. A more fanciful recom mendation was the brains of an electric ray mixed with alum and applied on the 16th day of the moon as a sure remedy for superfluous hairs! In the so-called electric eel there is a pair of .Mectnc generating organs one on each side of the tail. Their structure Is similar to that found in the electric w* the Columns con tabling the electric plates run lengthwise instead ?, * er ti«»Jllv, and the nerves supjilvin" i n,a - v he as manv as 2<»o in I tT^ r V a /' Se from tl,e s l'inal cord snstead of from the brain.

Men and Horses Knocked Down ..23. St .•£££". V 5 Cf the electric v„ a "- V are tolH 1 * „ Xu "»erous stories llti £ " V , of n.en and their rmVn h r-: ? knocked d ° w » thro« = i, while "f .-' 0 " taCt "Uh a " eJert ™ eei while fording a river. The African electric cat fi-h -rows m. to three feet in lencth but its shockis not nearly so powerful as in either i the ray or the so-called electric eel. j However, the shock* are sufficiently strong to cau-e ft»n-itJeraMe inconvenience to anyone handling the fish, an.J ' even quite small examples are said to be capable of giving distinct shocks. ,In the electric rat fish the elect riei generating organ instead of being m ade lip of hexagonal columns of plates, takes the form of a sheath of gelatinous material lying between the skin and the muscles, and enveloping the whole of. the trunk. The electric plates artscattered quite irregularly throughout this layer, and are placed transversely to the length of the body of the fish. It is indeed curious that this power of generating electricity has developed in four totally unrelated fishes, two being fresh-water and two marine.