portion to the dissimilarity of organs. The chief defect of this method consists in presupposing a knowledge of species and their organisation altogether beyond the existing stage of knowledge. It gives, however, distinct ideas of the degree of affinity subsisting between organised beings, independent of all physiological science. Until the appearance of this work, the Testacea had scarcely been made the subject of serious study. Adanson's methodical distribution, founded on not less than twenty of the partial classifications already alluded to, is decidedly superior to that of any of his predecessors. For the first time there was presented in this department of natural history a classification of the animals themselves, and not merely of the shells which contain them. Like every first attempt, however, it had its imperfections, which arose chiefly from ignorance of the anatomical structure of the animals. It was owing to this that he omitted, in his arrangement of the Mollusca, all molluscous animals without shells. He abandoned his original plan of publishing his Senegal observations in eight volumes, and applied himself entirely to his Families des Plantes, which he published in 1763. Here he developed the principle of arrangement above mentioned, which, in its adherence to natural botanical relations, was based on the system of Tournefort, and had been anticipated to some extent nearly a century before by Ray. The success of this work was hindered by its innovations in the use of terms, which were ridiculed by the defenders of the popular sexual system of Linnaeus; but it did much to open the way for the establishment, by means principally of Jussieu's Genera Plantarum (1789), of the natural method of the classification of plants. In 1774 Adanson submitted to the consideration of the Academy of Sciences an immense work, containing what may be called the universal application of his universal method; for it extended to all known beings and substances. This work consisted of 27 large volumes of manuscript, employed in displaying the general relations of all these matters, and their distribution; 150 volumes more, occupied with the alphabetical arrangement of 40,000 species; a vocabulary, containing 200,000 words, with their explanations; and a number of detached memoirs, 40,000 figures, and 30,000 specimens of the three kingdoms of nature. The committee to which the inspection of this enormous mass was intrusted strongly recommended Adanson to separate and publish all that was peculiarly his own, leaving out what was merely compilation. He obstinately rejected this advice; and the huge work, at which he continued to labour, was never published. He had been elected a member of the Academy of Sciences in 1759, and he latterly subsisted on a small pension it had conferred on him. Of this he was deprived on the dissolution of the Academy by the Constituent Assembly, and was consequently reduced to such a depth of poverty as to be unable to appear before the French Institute when it invited him to take his place among its members. Government afterwards conferred upon him a pension sufficient to relieve the simple wants of the great naturalist. He died, after months of severe suffering, on the 3d of August 1806, requesting, as the only decoration of his grave, a garland of flowers gathered from the 58 families he had differentiated—"a touching though transitory image," says Cuvier, "of the more durable monument which he has erected to himself in his works." His zeal for science, his unwearied industry, and his talents as a philosophical observer, are conspicuous in all his writings. The serenity of his temper, and the unaffected goodness of his heart, endeared him to the few who knew him intimately. On his return from Africa in 1754, he laid before the French Indian Company a scheme for the settlement of a colony in Senegal, where articles of African produce might be cultivated by free negroes. His propositions were unheeded by his countrymen, and by a misdirected patriotism he refused to present them to the Abolitionists of England. A similar feeling led him to refuse to settle in Austria, Russia, or Spain, on the invitation of the sovereigns of those countries. His most important works are his Natural History of Senegal and his Families of Plants. He contributed a number of papers to the Memoirs of the Academy of Sciences, on the Ship-worm, the Baobab tree (the largest tree known, to which, in honour of Adanson, Linnæus gave the name Adansonia digitata), the origin of the varieties of cultivated plants, gum-producing trees, and the Oscillatoria Adansonia, an animal regarded by him as a spontaneously moving plant. Besides these essays, he contributed several valuable articles in natural history to the earlier part of the Supplement to the first Encyclopédie; and he is also the reputed author of an essay on the Electricity of the Tourmaline (Paris, 1757), which bears the name of the Duke of Noya Caraffa.
Adaptation, in Biology, is the process by which an organism or species of organisms becomes modified to suit the conditions of its life. Every change in a living organ ism involves adaptation; for in all cases life consists in a continuous adjustment of internal to external relations. The term is usually restricted, however, to imply such modifications as arise during the life of an individual, when an external change directly generates some change of function and structure. Thus, since the adjustments of organ isms arise partly in direct response to causes acting on the individual, and partly in response to causes acting not directly on the individual but on the species as a whole, adaptation is to be regarded as the complement of natural selection. While natural selection acts primarily on the species, adaptation acts only indirectly, through the inheritance of modifications directly generated in the individual. All adaptation is limited, since an organ can only vary to a certain limited extent from its congenital structure. Adaptations are sometimes distinguished as indirect (for instance, by Haeckel, Generelle Morphologie, vol. ii.), which are directly generated in an organism, but only become apparent in its offspring. These form an important class, and seem to suggest that the phenomena of adaptation, thoroughly understood, would go far to explain all the difficult cases of so-called spontaneous variation.
Adda, the ancient Addua, a river of Northern Italy, formed by the union of several small streams, near the town of Bormio, in the Rhætian Alps, flows westward through the Valtellina into the Lake of Como, near its northern extremity. Issuing from the Lecco arm of the lake, it crosses the plain of Lombardy, and finally, after a course of about 150 miles, joins the Po, 8 miles above Cremona. The Adda was formerly the boundary between the territories of Venice and Milan; and on its banks several important battles have been fought, notably that of Lodi, where Napoleon defeated the Austrians in 1796.
Adder, the common viper (Vipera communis). The death adder (Acanthopis tortor) of Australia, and the puff adder (Clotho arietans) of South Africa, are both highly poisonous.
Addington, Henry, Viscount Sidmouth, prime minister of England, eldest son of Dr Anthony Addington, was born at Reading on the 30th May 1757. He was educated at Winchester and at Brazenose College, Oxford. In 1784 he was called to the bar at Lincoln's Inn, but being elected about the same time member of Parliament for Devizes, he did not enter on legal practice. He was already on terms of intimacy with the younger Pitt, his father having been Lord Chatham's medical adviser (a circumstance that secured for young Addington the nickname in Parliament of "the Doctor"); and he attached himself, as was natural, to the party of the great commoner.
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