Aristotle's History of Animals In Ten Books · Aristotle
CHAPTER VI.
1. The following are the principal classes which include other animals--birds, fishes, cetacea. All these have red blood. There is another class of animals covered with a shell, and called shell fish, and an anonymous class of soft-shelled animals (malacostraca), which includes carabi, carcini, and astaci; and another of mollusca, such as teuthis, teuthos, and sepia; and another class of annulose animals. All these are without blood, and the species with feet have many feet. There are no large classes of other animals; for there are many forms which are not included under a single form, but either stand alone, having no specific difference, as man, or have specific differences, but the classes are anonymous. 2. All animals with four feet and no wings have blood. Some of these are viviparous, others oviparous. The viviparous are not all covered with hair, but the oviparous have scales. The scale of a reptile is similar in situation to the scale of a fish. The class of serpents, sanguineous land animals, is naturally without feet. Though some have feet, this class is also covered with scales. All serpents, except the viper, are oviparous. The viper alone is viviparous, so that not all viviparous animals have hair; for some fishes also are viviparous. All animals, however, that have hair are viviparous; for we may consider the prickles of the hedgehog and porcupine as analogous to the hair of animals; for they answer the purpose of hair, and not, as in marine animals that are so covered, of feet.[25]
5. Our first subject of consideration must be the parts of which animals are made up, for these constitute the chief and the whole difference among them; either because they have them or are without them, or these parts vary in position or arrangement, or in any of the differences mentioned before, in form, size, proportion, and difference of accidents. First of all, then, we will consider the parts of the human body; for, as every one can best understand the standard of money with which he is most familiar, so it is in other things. And of necessity, man must be the best known to us of all animals. The parts of the body are, indeed, plain enough to every one's common sense; but, that we may not forsake our arrangement, and may have reason as well as perception, we will speak, first of all, of the organic, and afterwards of the simple, parts.
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