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Fishes. Fishes compose the fourth and last class of the backboned division of animals.

As it is necessary that their blood should be purified by coming in contact with air, they are provided with instruments, (the gills,) adapted for separating from the water the small quantity of air it has combined with it. The impure blood is then sent from the heart to the gills, over which it is distributed by numberless small bloodvessels ; water is received in at the mouth and forced out through the gills, and thus the air of the water and the impure blood are brought together.

As all the blood received by the heart is sent to the gills, the circulation is said to be double, as in the suckgivers and birds; but the quantity of air combined with the water being very small, the blood can imbibe but little oxygen; less perhaps than is imbibed by the blood of reptiles, in which only a part is sent to the lungs. Fishes, therefore, like reptiles, are cold blooded animals, and, as a consequence, their sensations, intelligence, and instincts, are comparatively feeble.

The element in which they live and move being nearly of the same weight as themselves, they do not require powerful limbs to enable them to rise. Many are provided with an air-bladder, by compressing or dilating which they make themselves heavier or lighter than their bulk of water, and are thus assisted in sinking or rising.

The principal instrument of motion is the tail-fin, which by its breadth, flexibility, vertical position, and situation, is adapted for propelling the fish forwards.

The fins on the back and belly serve to steady the fish, and the two on the breast tend to keep the head up, and assist the tail a little in giving the progressive motion.

The form of fishes, generally, is such as to offer the least possible surface to the water in front, and the scales with which they are covered always point backwards, and favour the same object.

Fishes, in general, have numerous teeth, always sharp and pointed, and often inclined towards the throat; they are used, not for chewing their food, (which is swallowed whole,) but for seizing and holding their slippery prey.

Fishes are arranged in two great divisions, the 1 bony and the cartilaginous. The former have a hard bony skeleton, whilst the cartilaginous have only a soft frame, or one containing little calcareous matter.

The osseous, or bony, are divided into six orders, according to the structure and arrangement of the fins. These are, the 8 thorny-rayed, as the perch; the * softrayed, as the carp, salmon, and herrings; the 5 softrayed, as the cod-fish and the flounder; the eel, wanting the ventral fins; the 7 tufted gills, as the sea-horse; and the & cheek-joined, as the globe-fish and sun-fish. · The cartilaginous have the calcareous matter in the form of grains, instead of filaments, or fibres, or plates, and the skeleton is formed of one piece, instead of distinct joints. This division consists of two orders, the 9 free-gilled, as the sturgeon, and the 10 fixed-gilled, as the shark and the lamprey.

The two divisions of the fourth class, Pisces-Fishes. 1 0s, a bone. 2. Chondropterygii, chondros, gristle, and pteryx, ray of a fin.

The six orders of the Osseous or hard-boned Skeletons. 3 Acanthopterygii, acantha, a thorn. | 6. Málacopterygii apodes, a, without, 4. Málacopterygii abdominales, malakos, 1 pous, a foot. soft, abdomen, the belly.

| 7. Lophobranchi, lophos, a tuft, and 5. Málacopterygii sub-brachiati, sub, branchiæ, the gills. under, and brachion, the arm. 8. Pléctognathi, plecto, to join, gnathos,

the jaw. 4, 5, and 6, are all soft-rayed, but they differ in the position or absence of the ventral fins.

The two orders of the Cartilaginous division. 9. Stariones, sturio, a sturgeon, or Chondropterygii branchis liberis, branchta, the gills, liber, free, open. 10. Chondropterygii branchis fixis, branchiæ, gills, fixus, fixed, immovable.

GREECE. From the Persian War to the Death of Epaminondas.

A bout five centuries before the Christian era, Darius, king of Persia, made war against Greece. His generals . invaded the country with a fleet of six hundred vessels, and half a million of men. There were scarcely any troops to oppose them, except ten thousand Athenians. The Athenian general was named Miltiades. He led his little army against the immense host of the Persians, and defeated them at Marathon. This was a small town on the sea-shore, about fifteen miles north-east of Athens.

After the battle of Marathon, the Persians were driven . out of Greece, and Darius died while he was preparing to invade the country again. His son Xerxes renewed the : war, and led into Greece the largest army ever collected together, amounting to upwards of 3,000,000; but being unsuccessful, he fled back to Asia, and thus ended the Persian invasion of Greece.

After the Persian war, Cimon, Aristides, and Pericles were the three principal men of Athens. Pericles at length became the chief person in the republic. Athens was never more flourishing than while he was at the head of the government. He adorned the city with magnificent

edifices, and rendered it famous for learning, poetry, and, works of art, such as temples, statues, and paintings. .

At this period a war commenced between Athens and Sparta. These were now the two principal states of Greece, and they had become jealous of each other's greatness. A fierce war followed, in which all the states of that part of Greece called ? Peloponnesus were en- ; ; gaged. This bloody strife lasted twenty-eight years,

1. Vide Root. 2. So called from Pelops its first king, now called Morea, from its numerous mulberry trees. 3. Of the two principal cities of Greece, Athens was walled and Sparta open; the Spartans believing that there was more s danger in such a protection than in a situation requiring incessant watchfulness.

The Peloponnesian war brought great misfortunes upon the Athenians. The Spartans conquered them, and burnt the city; and while this work of destroying the * walls was going forward, the 'victors caused gay tunes of music to be played. The Athenians were now placed under thirty Spartan captains; these were called the thirty tyrants of Athens, but they held their power only three years. Thrasybulus, a 'patriotic Athenian, then

incited his countrymen to regain their freedom. The thirty tyrants were 'expelled, and Thrasybulus was rewarded with a wreath made of two twigs of an olive tree, which was esteemed a great mark of honour. Athens again became prosperous, and its former government was restored in the year 403 before the Christian era.

Not long after this period, Thebes became the most distinguished city of Greece. It was the capital of the kingdom of Baotia. Epaminondas, the Theban general, was one of the best men that lived in ancient times; his private virtues were equal to his patriotism and valour. It is said of him, that a falsehood was never known to come from his lips; one of the greatest praises that can be bestowed on any man. He had, however, many enemies, and for a time was disgraced; but when war re-commenced, he was placed at the head of the army, with greater power than he had possessed before. The last victory that he gained was at Mantinea ; but it cost the Thebans dear, for while Epaminondas was fighting in the thickest of the battle, a Spartan soldier thrust a 'javelin into his breast. This event took place in the year 363 before the Christian era. After the death of Epaminondas the Thebans were no longer formidable to the rest of the Greeks.

GEOGRAPHICAL.-Write the names of the principal places in the Peloponnesus or

Morea. How were Corinth, Athens, Thebes, Delphos, and Doris situated ? What two gulfs nearly divided Greece into two parts ? CHRONOLOGICAL.- Pelopounesian war began B.o. 446. Death of Pericles, B.c. 429.


Earths and Fossils. Those substances known by the name of Earths are * nine in number, and are by chemists divided into alkaline earths, and earths proper. Two of the principal are lime and magnesia.

Lime is seldom found in a pure state; it is contained in chalk, which may be deemed a neutral salt, being formed by the combination of lime with carbonic acid. Lime is soluble in water, but in very small quantities ; more than 600 parts of water are necessary to dissolve one of it. It has a pungent, hot, and acrid taste; it turns blue vegetable colours green. It takes up water with 'avidity. When thrown into this liquid it splits, swells up, acquires a larger volume, and a great heat. It dissolves in acids without effervescence. Lime, when alone, is 'infusible, even though the fire may be urged by oxygen gas, as has been proved by Lavoisier ; but if combined with acids, it forms a fusible body. Of all these bases it is that most abundantly diffused throughout nature.

Magnesia has never yet been found free from every kind of foreign matter. To procure it in the utmost degree of purity, crystals of the sulphate of magnesia (Epsom salt), of which it forms the base, must be dissolved in distilled water, and decomposed by alkaline carbonates. Pure magnesia is exceedingly white, tender, and in appearance spongy. When perfectly pure it is not sensibly soluble in water. It excites no sensible savour on the tongue; and in this respect it is greatly different from lime.

1. Vide Root. 2. Vide page 140. 3. The study of fossils, geologi. cally, is very recent; perhaps the first hint was given about a century since by Mr. Smith, land surveyor, at Bath, who observed that the same kind of strata always gave the same kind of fossils, and thus identified both strata and fossils,

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