Aristotle shows a wide knowledge of animals. He dwells upon peculiar instincts, such as the migration of birds, the nest-building of the fish Phycis, the capture of prey by the fish Lophius, the protective discharge of ink by Sepia, and the economy of the hive-bee. He is fond of combining many particular facts into general statements like these: No animal which has wings is without legs; animals with paired horns have cloven feet and a complex, ruminating stomach, and lack the upper incisor teeth; hollow horns, supported by bony horn-cores, are not shed, but solid horns are shed every year; birds which are armed with spurs are never armed with lacerating claws; insects which bear a sting in the head are always two-winged, but insects which bear their sting behind are four-winged. He traces analogies between things which are superficially unlike, such as plants and animals—the mouth of the animal and the root of the plant. The systematic naturalist is prone to attend chiefly to the differences between species; Aristotle is equally interested in their resemblances. The systematic naturalist arranges his descriptions under species, Aristotle under organs or functions; he is the first of the comparative anatomists. His conception of biology (the word but not the thing is modern) embraces both animals and plants, anatomy, physiology, and system. That he possessed a zoological system whose primary divisions were nearly as good as those of Linnæus is clear from the names and distinctions which he employs; but no formal system is set forth in his extant writings. His treatise on plants has unfortunately been lost. Aristotle, like all the Greeks, was unpractised in experiment. It had not yet been discovered that an experiment may quickly and certainly decide questions which might be argued at great length without result, nor that an experiment devised to answer one question may suggest others possibly more important than the first. Deliberate scientific experiments are so rare among the Greeks that we can hardly point to more than two—those on refraction of light, commonly attributed to Ptolemy, and those by which Pythagoras is supposed to have ascertained the numerical relations of the musical scale. Aristotle was the last great man of science who lived and taught in Greece. His writings disappeared from view for many centuries, and when they were recovered they were not so much examined and corrected as idolised.