In two respects the work on Generation is worthy of more than a mere passing notice, and entitles its author to the possession of almost prophetic genius. The first is the enunciation of the great generalisation _omne vivum ex ovo_. Although this particular phrase is nowhere to be found, as is often erroneously stated, in the treatise on Generation, yet a perusal of Exercises I., LI., and LXII. will convince any one that Harvey had grasped this great idea, which has since been so abundantly verified. The other is his doctrine of _Epigenesis_, or the formation of the new organism from the homogeneous substance of the germ by the successive differentiation of parts, that all parts are not formed at once and together, but in succession one after the other. He put forward this doctrine of Epigenesis in contradistinction to that of _Metamorphosis_, according to which the germ was suddenly transformed into a miniature of the whole organism which subsequently grew. This is certainly very remarkable, and entitles him to be regarded as a forerunner of Caspar Wolff, Von Baer, and the modern Evolutionary School, which sees in the development of the organism from the ovum a passage from the homogeneous to the heterogeneous by a gradual process of differentiation, from a germ in which there is no sign of any of the parts of the adult to an organism with all its many and varied organs. Commenting on certain passages of Exercise XLV., in which Harvey specially refers to this subject, the late Professor Huxley remarked: “In these words, by the divination of genius, Harvey in the seventeenth century summarised the outcome of the work of all those who, with appliances he could not dream of, are continuing his labours in the nineteenth century.”[17] [17] Evolution: “Encyclopædia Britannica,” 9th ed. 1878. In addition to his long sojourn in Italy as a student, Harvey made several other visits to the Continent. In 1630 he consented to accompany the young Duke of Lennox in his travels abroad. He had returned by 1632, for in that year he was formally appointed physician to Charles I. Again, in 1636 he accompanied the Earl of Arundel on his embassy to the Emperor, and was absent some nine months. According to Aubrey, in 1649 Harvey, with his friend Dr. George Ent, again visited Italy. Some doubt has been thrown on this journey, but it receives support from a letter of Harvey’s to John Nardi, of Florence, written on November 30, 1653, in which he concludes by asking his correspondent to mention his name to his Serene Highness the Duke of Tuscany, “with thankfulness for the distinguished honour he did me when I was formerly in Florence.”