PDF - Wallace Online

472 TROPICAL NATUREDarwin had collected have never been made known. Thecause is well known to have been the continued pressure ofill -health. The work on Domesticated Animals was thusdelayed many years,after which came the labour of bringingout a much enlarged edition of the Origin of Species. TheDescent of Man was, apparently, at first intended to be acomparatively small book, but a difficulty connected with theorigin of the distinctive peculiarities of the two sexes led toan investigation of this subject throughout the animal kingdom.This was found to be of such extreme interest, and tohave such important applications, that its development withthe completeness characteristic of all the writer's work led tothe production of two bulky volumes, followed by anothervolume on the Expression of the Emotions in Man and Animals,not less instructive. None of Darwin's works has excitedgreater interest or more bitter controversy than that on man;and the correction of the numerous reprints, and of a finalenlarged edition in 1874, was found to be so laborious a taskas to convince him that any such extensive literary works asthose projected and announced six years previously must befinally abandoned. This, however, by no means impliedcessation from work. Observation and experiment were thedelight and relaxation of Darwin's life, 1 and he now continuedand supplemented those numerous researches on plantswe have already referred to. A new edition of an earlierwork on the Movements of Climbing Plants appeared in 1875 ;a thick volume on Insectivorous Plants in the same year;Cross and Self -Fertilisation in 1876 ;the Forms of Flowers in1877; the Movements of Plants, embodying much originalresearch, in 1880; and his remarkable little book on Earthwormsin 1881. This last work is highly characteristic ofthe author. In 1837 he had contributed to the GeologicalSociety a short paper on the formation of vegetable mouldby the agency of worms. For more than forty years thissubject of his early studies was kept in view ; experimentswere made, in one case involving the keeping a field untouchedfor thirty years, and every opportunity was taken of collectiAbout this time he said to the present writer : " When I am obliged togive up observation and experiment, I shall die." And he actually did continuehis experiments to within a few days of his death.