The muræna brings forth every month, while all the other fishes spawn only at stated periods: the eggs of this fish increase with the greatest rapidity.[2472] It is a vulgar[2473] belief that the muræna comes on shore, and is there impregnated by intercourse with serpents. Aristotle[2474] calls the male, which impregnates the female, by the name of “zmyrus;” and says that there is a difference between them, the muræna being spotted[2475] and weakly, while the zmyrus is all of one colour and hardy, and has teeth which project beyond the mouth. In northern Gaul all the murænæ have on the right jaw seven spots,[2476] which bear a resemblance to the constellation of the Septentriones,[2477] and are of a gold colour, shining as long as the animal is alive, but disappearing as soon as it is dead. Vedius Pollio,[2478] a Roman of equestrian rank, and one of the friends of the late Emperor Augustus, found a method of exercising his cruelty by means of this animal, for he caused such slaves as had been condemned by him, to be thrown into preserves filled with murænæ; not that the land animals would not have fully sufficed for this purpose, but because he could not see a man so aptly torn to pieces all at once by any other kind of animal. It is said that these fish are driven to madness by the taste of vinegar. Their skin is exceedingly thin; while that of the eel, on the other hand, is much thicker. Verrius informs us that formerly the children of the Roman citizens, while wearing the prætexta,[2479] were flogged with eel-skins, and that, for this reason, no pecuniary penalty[2480] could by law be inflicted upon them. CHAP. 40. (24.)—VARIOUS KINDS OF FLAT FISH. There is another kind of flat fish, which, instead of bones, has cartilage, such, for instance, as the raia,[2481] the pastinaca,[2482] the squatina,[2483] the torpedo,[2484] and those which, under their respective Greek names, are known as the ox,[2485] the lamia,[2486] the eagle,[2487] and the frog.[2488] In this number, also, the squali[2489] ought to be included, although they are not flat fish. Aristotle was the first to call these fish by the one generic name of σελάχη,[2490] which he has given them: we, however, have no mode of distinguishing them, unless, indeed, we choose to call them the “cartilaginous” fishes. All these fish are carnivorous,[2491] and feed lying on their backs, just as dolphins do, as already[2492] noticed; while the other fishes,[2493] too, are oviparous, this one kind, with the exception of that known as the sea-frog, is viviparous, like the cetacea.[2494] CHAP. 41. (25.)—THE ECHENEIS, AND ITS USES IN ENCHANTMENTS.