Only one year elapsed between the publication of the 'Descent of Man' and that of its next important successor, the 'Expression of the Emotions.' The occasion of this learned and bulky treatise in itself stands as an immortal proof of the conscientious way in which Darwin went to work to anticipate the slightest and most comparatively impertinent possible objections to his main theories. Sir Charles Bell, in one of the quaintly antiquated Bridgwater treatises--those marvellous monuments of sadly misplaced teleological ingenuity--had maintained that man was endowed with sundry small facial muscles solely for the sake of expressing his emotions. This view was so obviously opposed to the belief in the descent of man from some lower form, 'that,' says Darwin, 'it was necessary for me to consider it;' and so he did, in a lengthy work, where the whole subject is exhaustively treated, and Bell's idea is completely pulverised by the apt allegation of analogous expressions in the animal world. In his old age Darwin grew, in fact, only the more ceaselessly and wonderfully industrious. In 1875, after three years of comparative silence, came the 'Insectivorous Plants,' a work full of minute observation on the habits and manners of the sundew, the butterwort, the Venus's fly-catcher, and the various heterogeneous bog-haunting species known by the common name of pitcher plants. The bare mass and weight of the facts which Darwin had collected for the 'Origin of Species' might well-nigh have stifled the very existence of that marvellous book: it was lucky that the premature publication of Wallace's paper compelled him to hurry on his 'brief abstract,' for if he had waited to select and arrange the whole series of observations that he finally published in his various later justificatory volumes, we might have looked in vain for the great systematic and organising work, which would no doubt have been 'surcharged with its own weight, and strangled with its waste fertility.' But the task that he himself best loved was to watch in minute detail the principles whose secret he had penetrated, and whose reserve he had broken, working themselves out before his very eyes, naked and not ashamed--to catch Actæon-like the undraped form of nature herself in the actual process of her inmost being. He could patiently observe the red and slimy hair-glands of the drosera closing slowly and remorselessly round the insect prey, and sucking from their bodies with sensitive tentacles the protoplasmic juices denied to its leaves by the poor and boggy soil, on which alone its scanty rootlets can properly thrive. He could watch the butterwort curving round the edges of its wan green foliage upon the captured limbs of fly or aphis. He could note how the serried mass of finger-like processes in the utricles of the bladderwort slowly absorb organic matter from the larva of a gnat, or the minute water-insects entangled within its living and almost animated lobster-pot. He could track the