It has now been shown, though most briefly and imperfectly, how the law that "_Every species has come into existence coincident both in time and space with a pre-existing closely allied species_," connects together and renders intelligible a vast number of independent and hitherto unexplained facts. The natural system of arrangement of organic beings, their geographical distribution, their geological sequence, the phaenomena of representative and substituted groups in all their modifications, and the most singular peculiarities of anatomical structure, are all explained and illustrated by it, in perfect accordance with the vast mass of facts which the researches of modern naturalists have brought together, and, it is believed, not materially opposed to any of them. It also claims a superiority over previous hypotheses, on the ground that it not merely explains, but necessitates what exists. Granted the law, and many of the most important facts in Nature could not have been otherwise, but are almost as necessary deductions from it, as are the elliptic orbits of the planets from the law of gravitation. II. ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE ORIGINAL TYPE.[D] +--------------------------------------------------------------+ | [D] Written at Ternate, February, 1858; and published in the | | Journal of the Proceedings of the Linnaean Society for | | August, 1858. | +--------------------------------------------------------------+ _Instability of Varieties supposed to prove the permanent distinctness of Species._ One of the strongest arguments which have been adduced to prove the original and permanent distinctness of species is, that _varieties_ produced in a state of domesticity are more or less unstable, and often have a tendency, if left to themselves, to return to the normal form of the parent species; and this instability is considered to be a distinctive peculiarity of all varieties, even of those occurring among wild animals in a state of nature, and to constitute a provision for preserving unchanged the originally created distinct species.