grinding teeth; others, as the Sheep's-head, have the grinding surface convex; and others, as the genus Chrysophrys, have convex teeth so numerous and so closely packed over a broad surface, as to resemble the paving-stones of a street. The beautiful Chaetodons of warm climates, on the other hand, have teeth which resemble bristles, and these are set close together like the hairs of a brush; while the Perch of our own rivers has them still more slender, minute, and numerous, so as to resemble the pile of velvet. Another of our well-known fishes, the bold and fierce Pike, is armed with teeth scarcely less formidable in size, form, and sharpness, than the canines of a carnivorous quadruped. In number, also, there is a great variety. The Pike, the Perch, the Catfish, and many others, have the mouth crowded with innumerable teeth, while the Carp and the Roach have only a few strong teeth in the throat, and a single flat one above; and the Sturgeon, the Pipe-fish, and the Sandlaunce, are entirely toothless.

The eye in this Class presents a beautiful example of adaptation to the medium in which they live. From the density of water being so nearly the same as that of the aqueous and vitreous humours, these have scarcely any power to refract the rays of light; and hence a high magnifying power is given to the crystalline lens. Its form is that to which the very highest possible power is assigned— a perfect sphere, and the density of its texture is very great. But as the power of a lens and the nearness of its focal point are in the same ratio, it was needful to bring the retina, or curtain on which the image is painted, very close to the lens; and this is done by diminishing the vitreous humour behind it, and thus flattening the sphere; while a provision is made for maintaining this shape in certain plates of bone or cartilage, imbedded in the tough coat of the eye, called the sclerotica.

The eye is never protected by an eyelid in fishes; the pupil is very large and incapable of contraction; and another peculiarity is, that (at least in many species), the one eye is moved independently of the other.

The last organ we have space to notice at present is the air-bladder, which is found in most of the bony fishes. It is usually of a lengthened form, attached beneath the spine; but its shape is subject to some variety. Thus, in the Hedgehog fishes it is two-lobed, like a Dutchman's breeches; sometimes it is a double sac; in the great Carp family, and in the Electric Eels, it is divided into two compartments by a transverse partition, which, in the former case, is perforated to allow an intercommunication. In one of the Cat-fishes (Pangasius), it is divided into four compartments, and in others into many irregular cells. Thus, the airbladder closely approaches in structure the lowest form of the lung in air-breathing VERTEBRATA, as in the Axolotl and the Newts, in which this organ is a simple bladder, and in the Frogs and Toads, in which it is subdivided into large cells; and it may, therefore, be considered as the first rudimentary appearance of an aërial respiratory apparatus.

With regard to its function, in Fishes, it appears primarily to be connected with swimming. Being condensed by muscular pressure, or allowed to expand, it renders the body either heavier or lighter; and thus enables the fish to swim at any height in the water according to its pleasure. In general, the roving and surface-swimming species are furnished with the organ in question, while such as haunt the bottom are destitute of it; and this arrangement well agrees with the function we have ascribed to it. Yet it cannot be denied that there are some most unaccountable deviations from this rule. Thus, the Gurnards, which are ground-fishes, are well furnished with bladders; the two British species of Surmullet are deprived of the organ;

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while the Tropical species, which have the same habits, are provided with one. Again, of surface-fishes, our common Mackerel has no bladder, while the Spanish and Coly Mackerels, which have exactly the same manners, are each furnished with one.

In many cases the bladder is hermetically sealed, but in some instances it communicates by a tube with the stomach, or the gullet. The air which it contains appears to be a secreted gas; it is found to be, in some cases, oxygen, and in others, strange to say, nearly pure nitrogen. The former gas occurs chiefly in species that live in very deep water.

The blood, as already observed, is cold; that is, it commonly takes the temperature of the surrounding water; in some of the swift oceanic Fishes of the Mackerel family, however, such as the Tunny and the Bonito, the blood is found to be 10° higher than the temperature of the surface of the sea, even within the Tropics: the flesh of these Fishes is dark and dense. The blood-disks are sometimes circular, sometimes oval. They are larger than those of MAMMALIA and BIRDS; smaller than those of REPTILES, and especially than those of AMPHIBIA.

The irritability of the muscular fibre is considerable, and is long retained. Fishmongers take advantage of this property, to produce rigid muscular contraction, after life has ceased, by transverse cuts and immersion of the muscles in cold water: by this operation, which is called "crimping," the firmness and density of the muscular tissue are increased.

In our next paper, we may enter into some details of the instincts and habits of Fishes, and some other matters connected with the Class, of more popular interest than these structural peculiarities, which, we fear, will prove but a dry morsel to many of our readers.

P. H. G.

CAPTAIN WILLIAM COOK.

WILLIAM COOK was born at Greenock about the year 1788. His father commanded a vessel of his own, but died whilst his son was little more than an infant. The sailor's widow gave her little boy such schooling as her means could afford; and at ten years of age he left home for good and went to sea, and by the time he was thirteen years old his earnings were the chief support of his mother and two sisters. His mother had made him get by heart the Shorter Catechism with the Scripture proofs; and this, together with a certain influence from her own exhortations, he regarded as his chief preservative from evil. For although he was in some respects no better than other lads, he could never forget the Catechism and the Bible texts; and they, at least, kept him from drinking and the grosser immoralities. He was an excellent seaman. More espe

cially he was remarkable for cool bravery and daring. As he once told us, "I never knew fear. I heard people speak about being nervous, but I did not understand the feeling. Still it was only stoicism-a dogged contempt of death and danger; it was not the courage of a Christian." He had his own share of adventures. Whilst mate of a merchant vessel he fell into the hands of a press-gang, and served for two years and a half on board a man-of-war; and afterwards, whilst commanding a trader in the China Seas, he was taken by pirates, and made a narrow escape from being murdered on the spot. But probably his name would never have emerged above the level of the many intrepid and selfsacrificing men who conduct across the deep the wealth of England, had it not been for an incident that awakened much attention at the time, and of which the remembrance ought not to perish.

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In the end of February 1825, after being long detained by contrary winds, Captain Cook sailed away from Falmouth in command of the Cambria, a small vessel of 200 tons burden, with thirty-six miners on board, whom he was conveying to Vera Cruz. On the morning of the 1st of March he was overtaken by stormy weather in the Bay of Biscay, and was driven considerably out of his course. Whilst jogging on impatiently in a track which he was anxious to quit, he saw a large vessel bearing towards him under press of sail. At first he took little notice; but observing signals of distress flying at each mast-head, he hastened to render assistance. On drawing near he perceived that she had troops on board; and he saw what could not be fewer than five or six hundred persons crowded in the rigging and all along the hammock nettings. But it was not till within half-a-mile that, crossing her bows in order to take up a position to leeward, Captain Cook discovered thick volumes of smoke issuing from her ports, and saw too plainly that the stranger was on fire.

A boat soon came on board, and told him that this was the Kent East-Indiaman; that she had been burning for the last five hours; that the fire must now be near the powder-magazine; that she had on board from six to seven. hundred souls; and Captain Cook was asked how many of this number he could receive. "All! all!" was the instant answer of a British tar. But the rescue was attended with enormous difficulties. The guns of the merchant-warrior were loaded and shotted; and as the fire approached, they would discharge themselves to the imminent danger of the friendly deliverer. And, what was a much more fearful peril, there were 500 barrels of gunpowder, which any moment might scatter the mighty ship on the seething waters like the fragments of a filbert-shell. But Captain Cook sailed close up under the burning vessel's stern; and,