The profit derived from the sale of herrings at that time was so great that it soon became a special trade; it was, in fact, the regular practice of the Middle Ages for persons engaged in any branch of industry to unite together and form themselves into a corporation. Other speculators conceived the idea of bringing fresh fish to Paris by means of relays of posting conveyances placed along the road, and they called themselves _forains_. Laws were made to distinguish the rights of each of these trades, and to prevent any quarrel in the competition. In these laws, all sea-fish were comprised under three names, the fresh, the salted, and the smoked (_sor_). Louis IX. in an edict divides the dealers into two classes, namely, the sellers of fresh fish, and the sellers of salt or smoked fish. Besides salt and fresh herrings, an enormous amount of salted mackerel, which was almost as much used, was brought from the sea-coast, in addition to flat-fish, gurnets, skate, fresh and salted whiting and codfish. In an old document of the thirteenth century about fifty kinds of fish are enumerated which were retailed in the markets of the kingdom; and a century later the "Ménagier" gives receipts for cooking forty kinds, amongst which appears, under the name of _craspois_, the salted flesh of the whale, which was also called _le lard de carême_. This coarse food, which was sent from the northern seas in enormous slices, was only eaten by the lower orders, for, according to a writer of the sixteenth century, "were it cooked even for twenty-four hours it would still be very hard and indigestible." The "Proverbes" of the thirteenth century, which mention the freshwater fish then in vogue, also names the sea-fish most preferred, and whence they came, namely, the shad from Bordeaux, the congers from La Rochelle, the sturgeon from Blaye, the fresh herrings from Fécamp, and the cuttle-fish from Coutances. At a later period the conger was not eaten from its being supposed to produce the plague. The turbot, John-dory, skate and sole, which were very dear, were reserved for the rich. The fishermen fed on the sea-dragon. A great quantity of the small sea crayfish were brought into market; and in certain countries these were called _santé_, because the doctors recommended them to invalids or those in consumption; on the other hand, freshwater crayfish were not much esteemed in the fifteenth and sixteenth centuries, excepting for their eggs, which were prepared with spice. It is well known that pond frogs were a favourite food of the Gauls and Franks; they were never out of fashion in the rural districts, and were served at the best tables, dressed with green sauce; at the same period, and especially during Lent, snails, which were served in pyramid-shaped dishes, were much appreciated; so much so that nobles and bourgeois cultivated snail beds, somewhat resembling our oyster beds of the present day.