The problem of the genesis of species stated.--Nature of its probable solution.--Importance of the question.--Position here defended.--Statement of the DARWINIAN THEORY.--Its applicability to details of geographical distribution; to rudimentary structures; to homology; to mimicry, &c.--Consequent utility of the theory.--Its wide acceptance.--Reasons for this, other than, and in addition to, its scientific value.--Its simplicity.--Its bearing on religious questions.--_Odium theologicum_ and _odium antitheologicum_.--The antagonism supposed by many to exist between it and theology neither necessary nor universal.--Christian authorities in favour of evolution.--Mr. Darwin's "Animals and Plants under Domestication."--Difficulties of the Darwinian theory enumerated. The great problem which has so long exercised the minds of naturalists, namely, that concerning the origin of different kinds of animals and plants, seems at last to be fairly on the road to receive--perhaps at no very distant future--as satisfactory a solution as it can well have. But the problem presents peculiar difficulties. The birth of a "species" has often been compared with that of an "individual." The origin, however, of even an individual animal or plant (that which determines an embryo to evolve itself,--as, _e.g._, a spider rather than a beetle, a rose-plant {2} rather than a pear) is shrouded in obscurity. _A fortiori_ must this be the case with the origin of a "species." Moreover, the analogy between a "species" and an "individual" is a very incomplete one. The word "individual" denotes a concrete whole with a real, separate, and distinct existence. The word "species," on the other hand, denotes a peculiar congeries of characters, innate powers and qualities, and a certain nature realized indeed in individuals, but having no separate existence, except ideally as a thought in some mind. Thus the birth of a "species" can only be compared metaphorically, and very imperfectly, with that of an "individual." Individuals as _individuals_, actually and directly produce and bring forth other individuals; but no "congeries of characters" no "common nature" _as such_, can directly bring forth another "common nature," because, _per se_, it has no existence (other than ideal) apart from the individuals in which it is manifested. The problem then is, "by what combination of natural laws does a new 'common nature' appear upon the scene of realized existence?" _i.e._ how is an individual embodying such new characters produced? For the approximation we have of late made towards the solution of this problem, we are mainly indebted to the invaluable labours and active brains of Charles Darwin and Alfred Wallace.