leurs acces de coliere qui sont frequents surtout entre les males, leur
sentiment interieurs par ses efforts dirige plus fortement les fluides
vers cette partie de leur tete, et il s'y fait une secretion de matiere
cornee dans les uns (_Bovidae_) et de matiere osseuse melangee de matiere
cornee dans les autres (_Cervidae_), qui donne lieu a des protuberances
solides: de la l'origine des cornes, et des bois, dont la plupart de ces
animaux ont la tete armee.'

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.

In many cases a Linnaean species has been split up till it became, first,
a genus, then a family, and, in some cases, an order. What one naturalist
considers a species is considered by another a genus containing several
species, and, vice versa, the species of one authority is described as
merely a variety by another. The older naturalists might have said with
truth: we do not know what the species are, but we are quite certain that