[3] There is a tendency among writers on Variation, as affording the opportunity for the operation of Natural Selection, to assume that the variations presented by organisms are minute variations in every direction around a central point. Those observers who have done useful work in showing the definite and limited character of organic variations have very generally assumed that they are opposing a commonly held opinion that variation is of this equally distributed character. I cannot find that Mr. Darwin made any such assumption; and it is certain, and must on reflection have been recognized by all naturalists, that the variations by the selection and intensification of which natural selection has produced distinct forms or species, and in the course of time altogether new groups of plants and animals, are strictly limited to definite lines rendered possible, and alone possible, by the constitution of the living matter of the parental organism. We have no reason to suppose that the offspring of a beetle could in the course of any number of generations present variations on which selection could operate so as to eventually produce a mammalian vertebrate; or that, in fact, the general result of the process of selection of favourable variations in the past has not been _ab initio_ limited by the definite and restricted possibilities characteristic of the living substance of the parental organisms of each divergent line or branch of the pedigree. [4] See p. 62. [5] M. Paul Bourget of the Académie Française, is not only a charming writer of modern ‘novels,’ but claims to be a ‘psychologist,’ a title which perhaps may be conceded to every author who writes of human character. His works are so deservedly esteemed, and his erudition is as a rule, so unassailable, that in selecting him as an example of the frequent misrepresentation, among literary men, of Darwin’s doctrine, I trust that my choice may be regarded as a testimony of my admiration for his art. In his novel _Un Divorce_, published in 1904, M. Bourget, says: ‘La lutte entre les espèces, cette inflexible loi de l’univers animal, a sa correspondance exacte dans le monde des idées. Certaines mentalités constituent de véritables espèces intellectuelles qui ne peuvent pas durer à côté les unes des autres’ (Edition Plon, p. 317). This inflexible law of the animal universe, the struggle between species, is one which is quite unknown to zoologists. The ‘struggle for existence,’ to which Darwin assigned importance, is not a struggle between different species, but one between closely similar _members of the same species_. The struggle between species is by no means universal, but in fact very rare. The preying of one species on another is a moderated affair of balance and adjustment which may be described rather as an accommodation than as a struggle.