RAIA, the ray, in natural history, a ge nus of fishes of the order Cartilaginei. Generic character : five spiracles on each side, placed beneath, near the neck ; mouth beneath the head, transverse, be set with teeth ; head small, pointed, and not distinct from the body rbody some what rhomboidal. These fishes are found only in the salt water, where they feed on whatever animal substances they meet with. They are sometimes of the weight of two hundred pounds. They conceal themselves for the greater part of the winter in the mud or sand of the bottoms, and, in consequence of being unprovided with an air bladder, they are seldom seen near the surface of the water. The female is larger than the male, and produces her offspring living, and only one at a time ; the young extricating itself gradually from its confinement, and remaining some time attached by the umbilical ves sels, after its complete appearance. There are nineteen species.
R. batis, or the skate, is one of the largest of the genus, weighing sometimes two hundred pounds, and one of this size is reported to have been served up at St. John's College, Cambridge, England. It is the most esteemed species of the ge nus.
R. clavata, or the thorn-back, is much inferior to the skate in size and goodness. It inhabits the Mediterranean and other seas, and is distinguished by its long and curved spines, on its upper surface. The above are rhomboidal.
R. pastinaca, or the sting ray, inhabits the Indian and Mediterranean seas, and its tail is armed with a very long serrated spine, with which it can inflict very for midable wounds, and which it casts off every year. This was formerly supposed to contain the most subtle poison, and an cient naturalists have been extremely elegant and glowing in their descriptions on this subject. It injures, however, on ly by piercing and laceration, and, to pre vent this, the tail is almost always cut off as soon as the fish is caught. These fish es often lie in ambuscade, and seize their prey by surprise, and frequently take it by active and persevering pursuit.
R. torpedo, the torpedo, inhabits the Mediterranean and the North Seas, and grows to the weight of twenty pounds. This fish possesses a strong electrical pow er, and is capable of giving a very consi derable shock through a number of per sons forming a communication with it. This power was known to the ancients, but exaggerated by them with all the fa bles natural to ignorance, and it is only recently that the power has been ascer tained to be truly electric. It is conduct ed by the same substances as electricity, and intercepted by the same. In a mi nute and a half no fewer than fifty shocks have been received from this animal, when insulated. The shocks delivered
by it in air, are nearly four times as strong as those received from it in water. This power appears to be always voluntarily exercised by the torpedo, which occa sionally may be touched and handled without its causing the slightest agitation. When the fish is irritated, however, this quality is exercised with proportional ef fect to the degree of irritation, and its exercise is stated, in every instance, to be accompanied by a depression of the eyes. When the animal exerts that be numbing power from which it derives its name, and when it operates by separate and repeated efforts, this is always the case, both in the continued, and in the instantaneoui process, the eyes, which are at other times prominent, are with drawn into their sockets, a circumstance very naturally attaching both to the con densation and discharge of the subtle flu id. Specimens have been seen of this fish weighing fifty and even eighty pounds. It commonly lies in forty fa thom water, and is supposed to stupify its prey by this extraordinary faculty. It is sometimes nearly imbedded in the sands of shallows, and is stated, in these cases, to give to any one who happens to tread upon it, an astonishing and over whelming shock. On dissection, it was found to exhibit no, material difference from the general structure of the ray, excepting with respect to the electric or galvanic organs, which have been minute ly examined and detailed by the cele brated anatomist, John Ilunter. He states them "to be placed on each side of the cranium and gills, reaching thence to each great fin, and extending longitudi nally from the anterior extremity of the animal to the transverse cartilage which divides the thorax from the abdomen." From the whole description, it appears, that these organs, as Mr. Shaw observes, constitute a pair of galvanic batteries, disposed in the form of perpendicular hexagonal columns ; while, in the gym notus electricus, the galvanic battery is disposed lengthwise on the lower part of the animal. It is stated, that the torpedo, in its dying state, communicates shocks in more than usually rapid succession, but in proportional weakness, and in seven minutes, in these circumstances, three hundred and sixty small shocks were dis tinctly felt. On the same authority (that of Spallanzani) it is reported, that the young torpedo can exercise this power at the moment after its birth, and even pos sesses it while a fcetus, several of these having been taken from the parent fish, and been found to commmunicate per ceivable shocks, which, however, were more distinctly felt when these animals were insulated on a plate of glass.