GREEK BIOLOGY AND MEDICINE tion of every animal and every part of an animal, since everything that nature makes is a means to an end, and nature does nothing in vain. " It is evident that there must be something or other really existing, correspond- ing to what we call by the name of Nature. For a given germ does not give rise to any chance living being, nor spring from any chance one; but each germ springs from a definite parent and gives rise to a definite progeny. And thus it is the germ that is the ruling influence and fabricator of the off- spring." ^° The classification of living beings should take account, it would seem, both of their char- acteristics and of the processes by which they and their characteristics came into existence. In either case nature herself makes no break, admits no gap, in the whole scale of animate and inanimate being: " Nature proceeds little by little from things lifeless to animal life in such a way that it is impossible to determine the exact line of demarcation, nor on which side thereof an intermediate form should be. Thus, next after lifeless things in the upward scale comes the plant, and of plants one will differ from another as to its amount of apparent
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