(51.) The eggs[2772] of fishes grow in the sea; some of them with the greatest rapidity, those of the muræna, for instance; others, again, somewhat more slowly. Those among the flat fishes,[2773] whose tails or stings are not in the way, as well as those of the turtle kind, couple the one upon the other: the polypus by attaching one of its feelers to the nostrils[2774] of the female, the sæpia and loligo, by means of the tongue; uniting the arms, they then swim contrary ways; these last also bring forth at the mouth. The polypi,[2775] however, couple with the head downwards towards the ground, while the rest of the soft[2776] fish couple backwards in the same manner as the dog; cray-fish and shrimps do the same, and crabs employ the mouth. Frogs leap the one upon the other, the male with its fore-feet clasping the armpits of the female, and with its hinder ones the haunches. The female produces tiny pieces of black flesh, which are known by the name of gyrini,[2777] and are only to be distinguished by the eyes and tail; very soon, however, the feet are developed, and the tail, becoming bifurcate, forms the hind legs. It is a most singular thing, but, after a life of six months’ duration, frogs melt away[2778] into slime, though no one ever sees how it is done; after which they come to life again in the water during the spring, just as they were[2779] before. This is effected by some occult operation of Nature, and happens regularly every year. Mussels, also, and scallops are produced in the sand by the spontaneous[2780] operations of nature. Those which have a harder shell, such as the murex and the purple, are formed from a viscous fluid like saliva, just as gnats are produced from liquids turned sour,[2781] and the fish called the apua,[2782] from the foam of the sea when warm, after the fall of a shower. Those fish, again, which are covered with a stony coat, such as the oyster, are produced from mud in a putrid state, or else from the foam that has collected around ships which have been lying for a long time in the same position, about posts driven into the earth, and more especially around logs of wood.[2783] It has been discovered, of late years, in the oyster-beds,[2784] that the animal discharges an impregnating liquid,[2785] which has the appearance of milk. Eels, again, rub themselves against rocks, upon which, the particles[2786] which they thus scrape from off their bodies come to life, such being their only means of reproduction. The various kinds of fishes do not couple out of their own kind, with the exception of the squatina and the ray.[2787] The fish that is produced from the union of these two, resembles a ray in the fore part, and bears a name among the Greeks compounded of the two.[2788]