Aristotle's biology constantly seeking an order of progression corresponding to the excellence and amplitude of the equipment of each group of animals. The opening description, or division, of the parts of animals is so reduced to its simplest terms, and therefore so abstract that effort is needed to perceive its significance. " Of the parts of animals some are simple: to wit, all such as divide into parts uniform with themselves, as flesh into flesh; others are composite, such as divide into parts not uni- form with themselves, as, for instance, the hand does not divide into hands nor the face into faces." This distinction held good in Aristotle's time as now; ^' but the depth of its validity has been plumbed only through modern microscopic study of cells and tissues. So in regard to the classification of animals by genera and species which may be drawn from his writings. Altogether Aristotle refers to about five hundred and forty animals of all kinds, including insects; and yet modern zoology, recognizing more nearly one million species, largely preserves his classification. The attribute of soul or life and the degree and kinds of its efficient presence are with Aristotle the criterion of excellence in living
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