The _flesh_ of the sturgeon is firm, white, and of excellent flavour; and, by some persons, has been compared to veal. It is considered best when roasted; though it is commonly sold in a pickled state, and, in this state, is chiefly imported from the rivers of the Baltic and North America. All sturgeons that are caught near London are taken to the Lord Mayor, and are by him presented to the King. In Italy the _back bones_ of these fish are cut into pieces, salted and smoked for food. The Russians frequently convert the _skins_ of sturgeons into a kind of leather, which they use for the covering of carriages. 251. _The SHARKS and DOG-FISH_ (Squalus, Fig. 64) _constitute a tribe of sea-fish noted for their voracity, and peculiarly characterized by having, instead of gills, from four to seven breathing apertures, of curved form, on each side of the neck._ _They are found in all seas, and some of them are of enormous magnitude, measuring from twenty to thirty feet and upwards in length._ The _skins_ of nearly all these animals, which are rough, with hard and minute prickles, are in frequent use for polishing wood, ivory, and even iron. Those of the larger species are cut into thongs and traces for carriages; and, in Norway, a sort of leather is prepared from them, which is employed for shoes and many other purposes. The skin of the SPOTTED DOG-FISH (_Squalus canicula_) is converted into the well-known substance called _shagreen_, or _chagreen_. For this purpose it is extended on a board and covered with mustard seed; and, after having been exposed for several days to the effects of the weather, it is tanned. The best shagreen is imported from Constantinople. This is of brownish colour, and very hard; but when immersed in water, it becomes soft and pliable, and may be dyed of any colour. Shagreen is often counterfeited by preparing morocco leather in the same manner as the skins of the dog-fish. Such fraud may, however, easily be detected by the surface of the spurious manufacture peeling or scaling off, whilst that of the genuine article remains perfectly sound. Shagreen is employed principally to cover cases for mathematical instruments, and was formerly used for watch-cases and the covers of books. _Sharks' fins_ are an article of trade from the Arabian and Persian gulfs to India, and thence to China: they are generally packed in bales weighing each about 700 pounds. The _flesh_ of all the species of sharks is hard, and in general unpleasant both to the smell and the taste; yet it is sometimes eaten by seamen, after having been macerated for a while in water to soften it. The _eggs_ of sharks are also eaten. The _livers_ of all the species yield a considerable quantity of oil, which is useful for burning and for other purposes. From the livers of some of the larger kinds as much as seven or eight butts of oil have been obtained, worth twenty or thirty pounds and upwards.