This was the book, then, that the deeply afflicted author wrung from himself as his “testament.” It was written and printed with unprecedented speed. When the first copies were issued, the author had a feeling that he had nearly “done for himself.” He could not sleep. The state of his nerves gave great concern to his friends, who were watching him most anxiously. With a stolid fatalism, as if nothing mattered now, he yielded to their pressing advice, and decided to travel for a time. Far away on the blue Atlantic, at the gate to all the glories of the tropics, there is an island, Teneriffe, that was counted one of “the isles of the blest” in the old Roman days. A huge volcano rises from it, and on its flanks we find all the zones of the geography of plants, as in a model collection. Humboldt has given us a splendid description of it, as the first station of his voyage to the tropics. “The man who has some feeling for the beauty of Nature,” he says, “will find a more powerful restorative than climate on this lovely island. No place in the world seems to me better calculated to banish sorrow and restore peace to an embittered soul.” Haeckel went there. It was not an expensive journey, but it came as a fresh greeting from Nature. It was a new ocean after the long studies on the Mediterranean. What might it not afford in the way of medusæ and other zoological prizes when the general beauty of the landscape, that had enchanted Humboldt, had been fully enjoyed. With a mingling of his overflowing passion for Nature, and the gloomy fatalism that told him this would be his “last voyage” after his “last book,” he asked permission to leave Jena in the autumn of 1866, when the printing of the _Morphology_ was completed, and set out. It was no more to be his last voyage than the _Morphology_ to be his last testament. Although still subdued with resignation in his inner life, he came home in the spring of 1867 with a new elasticity of body and mind, restored by the influence of the palms and bananas and spurge, and braced for the great struggle of his life that was now to begin in earnest. The voyage had really two aims. To see the volcano above a palm-clad coast, with the Atlantic Ocean bringing its medusæ; and to work for Darwin.