楼主
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原文第一段:
THAT all higher animals are represented by distinct male and female forms is one of the most patent facts of obseration, striking enough in many a beast and bird to catch any eye, and familiarly expressed in not a few popular names which contrast the two sexes. In lower animals, the contrast, and indeed the separateness, of the sexes often disappears; yet even naturalists have sometimes mistaken for different species what were afterwards recognized to be but the male and female of a single form.