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Great good luck came to us when the first pair of eyes were invented, probably by the trilobite back in Silurian times; when the first ear appeared, probably in Carboniferous times; when the first pair of lungs grew out of a fish's air-bladder, probably in Triassic times; when the first four-chambered heart was developed and double circulation established, probably with the first warm-blooded animal in Mesozoic times.
The occurrence of hair, of a four-chambered heart which propels warm blood, of mammary glands, and of other systematic characters marks this species as a kind of mammal and not as a vertebrate in a section by itself.
If each of these classes had deliberated apart and acquired the right to assent to legislation as a separate body, a four-chambered parliament, such as existed in Sweden up to 1866 and still survives in Finland, would have been the result.
Its slow progress after that date is not difficult to understand. The advantage of a four-chambered heart and warm coat would be greatly reduced when the climate became warmer. The stimulus to advance would relax.
Under the plan adopted present public opinion as formulated in the results of the last election was not recognized as entitled to control the state senate. These changes in the state constitutions by which the executive and judicial branches of the government acquired the veto power amounted in practice to the creation of a four-chambered legislature.
In the latter part of the long period of cold it seems that some reptile exchanged its scales for tufts of hair, developed a four-chambered heart, and began the practice of nourishing the young from its own blood which would give the mammals so great an ascendancy in a colder world. Nor can we complain of any lack of evidence connecting the mammal with a reptile ancestor.
In the turtle it is so nearly complete that the venous and the arterial blood are fairly separated; in the crocodile it is quite complete, though the arteries are imperfectly arranged. Thus the four-chambered heart of the bird and mammal is not a sudden and inexplicable development. Its advantage is enormous in a cold climate.
Reptiles have a three-chambered heart, making them cold-blooded. Birds have a four-chambered heart, and a temperature higher than that of man. Reptiles left their eggs to hatch in the sun. Birds, by a fine instinct, built their nests with care. Some reptiles have 4 feet, some 2, some none. All birds have two feet.
Like the reptiles they lay tough-coated eggs and have a single outlet for the excreta, and they have a reptilian arrangement of the bones of the shoulder-girdle; like the mammals, they have a coat of hair and a four-chambered heart, and they suckle the young. Even in their mammalian features they are, as the careful research of Australian zoologists has shown, of a transitional type.
Somewhere along his line he picked up the four-chambered heart, the warm blood, the placenta, the diaphragm, the plantigrade foot, the mammary glands indeed, what has he not picked up on the long road of his many transformations? He left some of his superfluous forty-four teeth with his ancestral quadrumana of Eocene times, and kept thirty-two.
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