He had conceived the 'unity of organic composition,' meaning that there is only one plan of construction,--the same principle, but varied in its accessory parts. In 1830, when Geoffroy proceeded to apply to the Invertebrata his views as to the uniformity of animal composition, he found a vigorous opponent in Cuvier. Geoffroy, like Goethe, held that there is in Nature a law of compensation, or balancing of growth, so that if one organ take on an excess of development, it is at the expense of another part; and he maintained that, since Nature takes no sudden leaps, even organs which are superfluous in any given species, if they have played an important part in other species of the same family, are retained as rudiments, which testify to the permanence of the general plan of creation. It was his conviction that, owing to the conditions of life, the same forms had _not_ been perpetuated since the origin of all things, although it was not his belief that existing species were becoming modified. Cuvier, on the other hand, maintained the absolute invariability of species, which, he declared, had been created with regard to the circumstances in which they were placed, each organ contrived with a view to the function it had to fulfil,--thus putting the effect for the cause ('Encyclopædia Britannica,' 9th edition, vol. xxi., p. 171). GEORGE CUVIER was born in 1769 at Montbéliard, in the department of Doubs, which at that time belonged to Württemberg. He was educated at Stuttgart, and studied political economy. While acting as private tutor to a French family in France he followed his favourite pursuit, the study of natural sciences. Geoffroy Saint-Hilaire heard of him, and appointed him assistant in the department of comparative anatomy in the Musée d'Histoire Naturelle. In 1799 he was elected Professor of Natural History at the Collège de France, and soon after he became Perpetual Secretary of the Institut National. In 1831, a year before his death, Louis Philippe raised him to the rank of a peer of France. Cuvier was the first to indicate the true principle upon which the natural classification of animals should be based--namely, their structure. It is the study of the anatomy of the creatures and their comparison which affords the only sound basis of a classification. The work which had the greatest influence upon the scientific public is his 'Règne animal distribué d'après son Organisation,' 1817. The system which he propounded in this book gradually came to have almost world-wide fame, and, in spite of its many obvious deficiencies, still lingers in some of our most recent text-books.