Page:Greek Biology and Medicine.djvu/75

 Aristotle's biology These famous passages may be taken as indicating Aristotle's view of the graded order- ing of life^ with reference to the phenomena exhibited by living beings after they are formed. The processes of their generation were likewise graded in accordance with the nature of the animal. This graded change in the manner of generation, more than any other fact, seems to have determined Aristotle's classification of animals. Doubtless a similarity in obvious organic structure led men to recognize the larger natural divisions, like birds and fishes. Such generic likenesses, with due account taken of evident as well as more subtle differences, might be followed in forming conceptions of subordinate groups. But to the mind searching for criterions of identity or distinction, nothing is more taking than the ways in which animals reproduce their kind. So felt this profound student of life. Perhaps no other man has ever discovered so many interesting facts touching the production of the young within and without the womb. Of course he stood but at the threshold of embryology. He had no micro- scope. The myriad facts which the studies of the last two centuries have elicited were un- [53]