parts, is fashioned by its final cause through a process of generation. Even when mature, it is not a static being, but still a vital process, living its life, its full life which it had not attained as an embryo. The embryo has the nutritive soul or life, but not the sensitive and motor soul which comes at birth, and still less the rational soul which comes to man alone.
"For nobody would put down the unfertilized embryo as soulless or in every sense bereft of life (since both the semen and the embryo of an animal have every bit as much life as a plant). . . . That then they possess the nutritive soul is plain. ... As they develop, they also acquire the sensitive soul, in virtue of which an animal is an animal. ... An animal does not become at the same time an animal and a man and a horse or any other particular animal. For the end is developed last, and the peculiar character of the species is the end of the generation of each individual."46 This passage states a fundamental principle of embryology, that the general characters belonging to the class or genus are first displayed by the embryo, and afterwards the distinguishing characters of the species to which it belongs.47
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