 Within the confines of the Muséum, parallel, if not immediately continuous, developments of related issues bearing on species transformism were made by Lamarck’s younger colleague and holder of the chair of Mammals and Birds, the comparative anatomist Etienne Geoffroy St. Hilaire (1772–1844). Less concerned with the issue of species transformism than with the implications of comparative anatomy for the relations of forms, Geoffroy St. Hilaire explored the anatomical “unity of type”—the remarkable resemblance of anatomical structure between organisms revealed by comparative anatomy. Pursuing this issue in his Muséum lectures and in several papers, Geoffroy St. Hilaire proceeded to work out the implications of the inner anatomical similarities of vertebrates. Based upon two main principles, the “principle of connection” and the “law of balance”, Geoffroy St. Hilaire drew attention to the implications of comparative anatomy for the unity of the animal kingdom. In the mid-1820s, Geoffroy St. Hilaire developed a more historical position on the relation of the unity of type to issues of the fossil record and to the development of life (Le Guyader 1998 [2004: chp. 4]).