In 1881 he made the second longest journey of his life. He secured permission to absent himself from the university for six months, and went to Ceylon. He left Jena on the 8th of October, and did not return until April 21, 1882. The traveller and æsthete in him revelled in this first plunge into the tropics. How he was taken to the enchanted land of India in the Lloyd steamer _Helios_, a pretty reminiscence of the “heliozoa” (sun-plants), a name he had himself invented; how he greeted his beloved medusæ in their beautiful tropical forms of the Indian Ocean; how he lived in the execrable but thoroughly tropical and interesting Whist-Bungalow at Colombo, where mysticism and an unholy joy in card-playing occupied him until philosophic zoology came to crown and redeem everything; how he set up his zoological laboratory far from the world at the Cingalese village of Belligemma (which he interpreted _bella gemma_, the “pretty jewel”), and fished with his Müller-net for radiolaria, medusæ, and siphonophoræ, for six whole weeks, to the intense bewilderment of the naked children of the palms; how he at last penetrated into the wildest virgin forests of Ceylon, where one heard the heavy tread of the elephant and the roar of the panther—all this he has described in his _Visit to Ceylon_, the freshest expression of his temperament, which belongs utterly to the free, artistic half of his life, when Persephone has her summer days in the land of flowers. He himself regarded this journey, happy and favoured to the very last minute, as a crown and conclusion of his travels that could never be surpassed. But many a long hour was to be spent in travel after that, and he was to make one journey that left Ceylon far behind him in the Indian Ocean. In the spring of 1887 he made a pilgrimage to the “Holy Land,” Jerusalem and the Dead Sea, Damascus and Lebanon. On this journey he spent a delightful month on the island of Rhodos. In 1889 he had a pleasant time on the beautiful island of Elba. In 1890 he visited Algiers, where his innocent sketches and his anatomical knife brought suspicion on him; they arrested him and threatened to shoot him as a spy. He has described the incident in his genial way in his _Algerian Reminiscences_ which is, unfortunately, lost in a back number of some magazine or other, like so many of the sketches of his travels. In 1897 he travelled over the whole of Russia, from Finland to the Caucasus, and visited Tiflis, Colchis, and the Crimea. In the autumn of 1892 he accompanied Sir John Murray, of the _Challenger_ expedition, on a small deep-sea investigation on the coast of Scotland. In the spring of 1893 and 1897 he was at work once more in his beloved Messina, where he was now honoured as a world-famous guest. In the autumn of 1899 he climbed the Sabine and Corsican hills. As the second decade after his first journey to the tropics came to an end, he seemed to regard all he had done so far as a small payment on account.