His caution to her about the sharks hadn't discouraged her, though, as he had intended.
Internally they are found to consist of a lamina twisted upon itself, and externally they generally exhibit a tortuous structure, produced, before the cloaca was reached, by the spiral valve of a compressed small intestine (as in skates, sharks and dog-fishes); the surface shows also vascular impressions and corrugations due to the same cause.
Of the cartilaginous fishes, Chondropterygii, the true sharks and hammer-headed sharks, are numerous.
Besides the commoner kinds of fishes, sharks, the torsk, opah and sunfish occur.
Of the sharks the genus Squalus is represented by individuals that grow to a length of 26 to 30 ft.
They include shad, rock cod, mackerel, mullet, bream and soles; sharks, stingrays, cuttlefish and the octopus are also common in the waters off the coast of Natal.
This elaborate type of scolex appears to be an adaptation to grasp the spiral intestinal valve of sharks and rays.
The dredge often brings up large numbers of nodules formed upon sharks' teeth, the ear-bones of whales or turtles or small fragments of pumice or other volcanic ejecta, and all more or less incrusted with manganese oxide until the nodules vary in size from that of a potato to that of a man's head.
The manganese nodules afford the most ample proof of the prodigious period of time which has elapsed since the formation of the red clay began; the sharks' teeth and whales' ear-bones which serve as nuclei belong in some cases to extinct species or even to forms derived from those familiar in the fossils from the seas of the Tertiary period.
Besides chipped stone knives, the teeth of rodents, sharks, and other animals served an excellent purpose.
The Oamaru limestones have been largely used for building stones; they are a pure white limestone, largely made up of foraminifera, bryozoa and shell fragments, and contain the teeth of sharks (e.g.
Sharks are found everywhere and are common round the north, though they rarely attack man.
Over a large part of the central Pacific, far removed from any possible land-influences or deposits of ooze, the red-clay region is characterized by the occurrence of manganese, which gives the clay a chocolate colour, and manganese nodules are found in vast numbers, along with sharks' teeth and the ear-bones and other bones of whales.
Smith Woodward has observed that the decline of many groups of fishes is heralded by the tendency to assume elongate and finally eel-shaped forms, as seen independently, for example, among the declining Acanthodians or palaeozoic sharks, among the modern crossopterygian Polypterus and Calamoichthys of the Nile, in the modern dipneustan Lepidosiren and Protopterus, in the Triassic chondrostean Belonorhynchus, as well as in the bow-fin (A7nia) and the garpike (Lepidosteus).
Many fish inhabited the Carboniferous seas and most of these were Elasmobranchs, sharks with crushing pavement teeth (Psammodus), adapted for grinding the shells of brachiopods, crustaceans, &c. Other sharks had piercing teeth (Cladoselache and Cladodus); some, the petalodonts, had peculiar cycloid cutting teeth.
Most of the sharks lived in the sea continuously, but the ganoids frequenting the coastal waters appear to have migrated inland.
Sharks' teeth, shells and bamboo were formerly generally used as cutting instruments for shaving and surgical operations.
Sharks are caught in enormous numbers with hook and harpoon; the flesh is considered by some to have aphrodisiacal properties; the dried fins and tails are exported to China; the oil is used for smearing boats.
A two-edged weapon, of which the blade is of sharks' teeth, and a defensive armour of braided sennit, are also peculiar to the islands; a large adze, made of the shell of the Tridacna gigas (the largest bivalve known), was formerly used in the Carolines, probably by the old builder race.
Sharks infest the estuaries.
The chief products for export are copra, tortoise-shell, mother-of-pearl, sharks' fins and trepang.