First, then, he examined the varieties of MAMMALIA. The mammalia, of which man himself is the highest type, are the leading class of the great order of vertebrate, or back-boned animals, and fishes are the lowest, the intermediate classes being birds and reptiles. VERTEBRATA are of higher rank in the animal kingdom than the mollusca, or soft-bodied animals, those having "red blood and a double-chambered heart." The mammalia are the class which suckle their young; second to them are the BIRDS; and then the blood cools, the organisation is inferior, and the REPTILES are produced; and lastly come the FISHES, with cold blood, and wanting aerial lungs. Philosophers, who have settled the scheme of the world as one of progression, complication, or development, trace animal life from the polypus, (which belongs to the order of Radiata, or animals that have a central point in which the vital force of the animal appears to preside, diverging in radii, as in the sea-eggs, starfishes, coral, sponges); the polypus advances to the Articulata, or jointed animals, including all kinds of worms, leeches, or ringed animals, of which insects are the most highly organised developments; next to the Mollusca, or soft-bodied animals; and then from these, which include the shell-fish, the scheme gradually progresses to the fish with backbones; and here the lowest order of Vertebrata is developed: the fish merges into the reptile, the reptile into the bird; the bird, as in the ornithorhyncus, into the Mammalia. Thus the gradations of life may be clearly apprehended by the visitor. The highest development of animal life he has seen in the MAMMALIA SALOON, all the animals of which produce their young alive and suckle them; the order of life immediately below the mammalia, he has examined in the marvellous varieties of birds arranged in the NORTHERN GALLERY; then he turned to the west, and examined the third order of animal life in the REPTILES; then the fourth order represented by FISH; and so on till he watched the simpler forms of life in the STAR-FISH and the SPONGE.