[1] The greatest anatomists, and especially Mr. Owen, have recently expressed their conviction, that researches on the structure of animals must be guided by the principle of _unity of composition_ as well as the principle of _final causes_. See Owen _On the Nature of Limbs_. [2] This has been termed by physiologists _The Law of the Development from the General to the Special_. [3] Every reader of physiological works knows how easy it would be to multiply examples of this kind to any extent. Thus it is held by physiologists, that the sporules of fungi are universally diffused through the atmosphere, ready to vegetate whenever an opportunity presents itself: and that a single individual produces not less than ten millions of germs. It is held also that innumerable seeds of plants still capable of vegetation, lie in strata far below the earth's surface, finding the occasion to vegetate only by the rarest and most exceptional occurrences.--Carpenter, _Manual of Physiology_. 1851, Art. 44. [4] Chalmers, p. 35. [5] Ibid. p. 21 [6] Ibid. p. 119. [7] Dr. Scoresby, in his _Account of the Arctic Regions_ (1820) Vol. II. has given figures of 96 such forms, selected for their eminent regularity from many more. CHAPTER XII. THE UNITY OF THE WORLD. 1. The two doctrines which we have here to weigh against each other are the Plurality of Worlds, and the Unity of the World. In so saying, we include in our present view, a necessary part of the conception of a _World_, a collection of intelligent creatures: for even if the suppositions to which we have been led, respecting the kind of unintelligent living things which may inhabit other parts of the Universe, be conceived to be probable; such a belief will have little interest for most persons, compared with the belief of other worlds, where reside intelligence, perception of truth, recognition of moral Law, and reverence for a Divine Creator and Governor. In looking outwards at the Universe, there are certain aspects which suggest to man, at first sight, a conjecture that there may be other bodies like the Earth, tenanted by other creatures like man. This conjecture, however, receives no confirmation from a closer inquiry, with increased means of observation. Let us now look inwards, at the constitution of man; and consider some characters of his nature, which seem to remove or lessen the difficulties which we may at first feel, in regarding the Earth as, in a unique and special manner, the field of God's Providence and Government.