The Siboga Expedition ended in Surabaya on 26 February 1900; it had lasted for almost one year. The most difficult and time-consuming work had still to be done, viz. the study of the material, the elaboration of the hydrographical data, and the publication of the results.

In the year before the expedition started, in 1898, Weber had resigned his ordinary professorship to become Extraordinary Professor again, but he remained Director of the Zoological Museum. Beside him, Carl Philip Sluiter had been appointed Ordinary Professor of general Zoology. This gave him more time to work on and edit the results of the expedition in his house at Eerbeek. In Fig. 19 we see him in his laboratory at the Zoological Museum in Amsterdam with his staff.

The results of the Siboga Expedition appeared to surpass all expectations (Weber, 1904b; De Beaufort, 1963). It appeared that especially the coastal fauna of the Indo-Australian Archipelago displays a richness and diversity of species, unsurpassed by any other region of the earth. This can be explained by the fact that these coasts are broken into many islands and one knows that isolation is an important factor in speciation. This isolation also occurs in closed deep-sea basins, and therefore the results of the Siboga Expedition could equal the results of expeditions around the world: about one half to one third of the species sampled by the Siboga appeared to be new to science.

Weber worked very hard: from the cover of the first monograph in the seriesSiboga Expeditie (containing his narrative and the list of stations revised by Tydeman, published January 1902: Weber, 1902; Tydeman, 1902a) it appears that 65 monographs had been envisaged at the outset. Conspicuous among the many Siboga reports are Max Weber's own on the fishes (both marine and freshwater) and on the cetaceans (Weber, 1913; 1923), and his wife's on the coralline Algae (Weber-van Bosse & Foslie, 1904; Weber-van Bosse & Reinbold, 1913; Weber-van-Bosse, 1921; 1923; 1928). Anna Weber dedicated her great work on the Algae of the Siboga Expedition to Professor Hugo de Vries (Weber-van Bosse, 1928: v). In 1910 the honorary degree of Doctor of Science was bestowed upon her by the University of Utrecht. She thus became the first woman ever honoured with the degree of Doctor honoris causa in The Netherlands (Buisman, 1935). Max Weber dedicated his great work on the fishes of the Siboga Expedition to his wife. I quote him in translation (Weber, 1913: v): "who has been always a joyful and helpful travelling-companion to me, in the extreme North, in South Africa, in the Indo-Australian Archipelago and also during the Siboga Expedition". In his later years, with the help of his pupil and successor, Professor L. F. de Beaufort, Weber undertook the task of setting in order the whole Indo-Australian fish fauna, of some three thousand species in all. Of this great and laborious work eleven volumes have appeared (Weber & De Beaufort, 1911-1962).

In the midst of all these undertakings Max Weber had found the time to contribute extensively to a textbook called Lehrbuch der Biologie für Hochschulen co-authored by Moritz Nussbaum and Georg Karsten, published in 1911 (second edition 1914). He wrote the section on the biology of animals, and here we can see that Weber was also interested in ecology, physiology, embryology, etc. In these respects it is really a modern textbook, one of the first of its kind (cf. De Visser, 1984).

Weber retired in 1921 and by the time he died in 1937 about 95% of the scientific results of the Siboga Expedition had been published. At present, the work is nearly completed, as only the following groups are still being treated: Asteroidea, some groups of Decapoda Brachyura, and some holoplanktonic groups.**

Max Weber was a childless man, but he had everything else that should accompany old age. He was rich in honours. He had both charm and dignity, though some called him a potentate (cf. our interviews with Professor H. Engel and other old pupils of Max Weber; De Visser, 1984: 3-4), and he enjoyed for many years such general admiration and esteem as are only given to the very best of men. In 1922, when he reached his 70th birthday (Fig. 20; this photograph was probably made on that occasion), a special volume of Bijdragen tot de Dierkunde (vol. 22) was dedicated to him. Moreover, a letter was sent to him by a number of English zoologists, which was published in Nature (Thomson et al., 1922). They spoke with unaccustomed warmth, saying in conclusion: "Your solid learning has upheld the great scientific traditions of your country, your investigations have influenced and stimulated many of us, your broad interests, your singleness of purpose, the simplicity of your life and your genius for friendship have set an example to us all."

Max Weber died on 7 February 1937 and Anna Weber on 29 October 1942. They bequeathed their estate at Eerbeek to the foundation "Het Gelders landschap". Their house, that was built on the foundations of a castle that once belonged to the counts of Gelre, nowadays functions as an adult education centre. Max Weber donated his library and his scientific correspondence to the library of the Royal Zoological Society Natura Artis Magistra (now Artis Library, University of Amsterdam) and to the Zoological Museum (now called Institute of Taxonomic Zoology (Zoological Museum), University of Amsterdam). His bibliography has been published by De Beaufort (1937; five additional references to Weber's body of work are given by De Visser, 1984: 12-13). Anna Weber donated her herbarium of about 50,000 specimens to the Rijksherbarium at Leiden (Koster, 1942). Her bibliography has been published by Koster & Van Benthem Jutting (1942).

** In our library we always use the prospectus (De Beaufort, 1963) issued by Brill to find our way in the bibliographical babel called Siboga Expeditie. Since De Beaufort's death in 1968, the series is edited by his successor at the University of Amsterdam, Jan H. Stock. Two more Siboga Expeditie monographs have been published since 1963 (Pettibone, 1970 and Griffin & Tranter, 1986).