It is demonstrated by Mr. Darwin's careful weighings and measurements, that, though little used parts in domestic animals get reduced in weight and somewhat in size, yet that they show no inclination to become truly "rudimentary structures." Accordingly he asserts[94] that such {103} rudimentary parts are formed "suddenly, by arrest of development" in domesticated animals, but in wild animals slowly. The latter assertion, however, is a _mere assertion_; necessary, perhaps, for the theory of "Natural Selection," but as yet unproved by facts. But why should not these changes take place suddenly in a state of nature? As Mr. Murphy says,[95] "It may be true that we have no evidence of the origin of wild species in this way. But this is not a case in which negative evidence proves anything. We have never witnessed the origin of a wild species by any process whatever; and if a species were to come suddenly into being in the wild state, as the Ancon Sheep did under domestication, how could you ascertain the fact? If the first of a newly-begotten species were found, the fact of its discovery would tell nothing about its origin. Naturalists would register it as a very rare species, having been only once met with, but they would have no means of knowing whether it were the first or the last of its race." To this Mr. Wallace has replied (in his review of Mr. Murphy's work in _Nature_[96]), by objecting that sudden changes could very rarely be useful, because each kind of animal is a nicely balanced and adjusted whole, any one sudden modification of which would in most cases be hurtful unless accompanied by other simultaneous and harmonious modifications. If, however, it is not unlikely that there is an innate tendency to deviate at certain times, and under certain conditions, it is no more unlikely that that innate tendency should be an harmonious one, calculated to simultaneously adjust the various parts of the organism to their new relations. The objection as to the sudden abortion of rudimentary organs may be similarly met. Professor Huxley seems now disposed to accept the, at least {104} occasional, intervention of sudden and considerable variations. In his review of Professor Koelliker's[97] criticisms, he himself says,[98] "We greatly suspect that she" (_i.e._ Nature) "does make considerable jumps in the way of variation now and then, and that these saltations give rise to some of the gaps which appear to exist in the series of known forms." [Illustration: MUCH ENLARGED HORIZONTAL SECTION OF THE TOOTH OF A LABYRINTHODON.]