Lamarck's actual words (_Phil. Zool.,_ edit. 1873, p. 254) are: 'Dans leurs accès de colière qui sont fréquents surtout entre les mâles, leur sentiment intérieurs par ses efforts dirige plus fortement les fluides vers cette partie de leur tete, et il s'y fait une secrétion de matière cornée dans les uns (_Bovidae_) et de matière osseuse mélangée de matière cornée dans les autres (_Cervidae_), qui donne lieu à des protubérances solides: de là l'origine des cornes, et des bois, dont la plupart de ces animaux ont la tête armée.' Darwin, on the other hand, definitely set before himself the problem of the origin of species, which the majority of naturalists, in spite of Lamarck and his predecessor Buffon, regarded as permanent and essentially immutable types established by the Creator at the beginning of the world. This principle of the persistence and fundamentally unchangeable nature of species was regarded as an article of religion, following necessarily from the divine inspiration of the Bible. This theological aspect of the subject is sufficiently curious when we consider it in relation to the history of biological knowledge, for Linnaeus at the beginning of the eighteenth century was the first naturalist who made a systematic attempt to define and classify the species of the whole organic world, and there are few species of which the limits and definition have not been altered since his time. In fact, at the present time there are very numerous groups, both in animals and plants, on the species of which scarcely any two experts are agreed.