During the year 1859 he travelled as medical man and artist in Sicily. In 1861 he was induced by Gegenbaur, whose acquaintance he had made in Würzburg, to establish himself as a _Privat-docent_ for comparative anatomy in Jena. And there he has remained ever since, filling the Chair of Zoology, and having declined several much more tempting offers from the Universities of Würzburg, Vienna, Strassburg, and Bonn. Within one year, 1865, he wrote the two volumes of his 'Generelle Morphologie der Organismen,' as he himself relates, in order to master his sorrow over the loss of his first wife. But he broke down, and went to the Canaries to recruit health and strength. The 'Morphologie,' which has long been out of print,[25] made scarcely any impression. It was ignored, probably because he had placed the old-fashioned study of zoology and morphology upon a thoroughly Darwinistic basis. [25] That this great work is now comparatively rare, although still in the second-hand market, may perhaps be urged in excuse of the fact of so many attempts made by many authors, both professional and amateur, to find fault with or to explain the principles of adaptation, variation, heredity, cænogenesis, phylogeny, etc., in complete ignorance that all these and many more fundamental questions were fully discussed more than thirty years ago in the 'Generelle Morphologie.' On the advice of his friend Gegenbaur, he gave a more popularly written abstract of his 'Generelle Morphologie'--in fact, the substance of a series of his lectures--in the shape of his 'Natürliche Schöpfungsgeschichte.' This 'History of Natural Creation,' which in 1898 has reached the ninth edition (first edition translated into English in 1873), had the desired effect. So also had his 'Anthropogenie oder Entwicklungsgeschichte des Menschen,' the fourth edition of which appeared in 1891. It was a lucky coincidence that Haeckel had just finished his preliminary academical studies, was entirely at leisure, and undetermined to which branch of natural science he should devote his genius, when Darwin's great work was given to the world. Haeckel embraced the new doctrine fervently, and, as Huxley was doing in England, he spread it and fought for it with ever-increasing vigour in Germany.