ORGANIC POLARITY AND MUTATION 105 



Mr. Thornton) the black shouldered kind had increased " to the 

 extinction of the previously existing breed." 



Then, again, as J. J. Murphy says ' : — "The otter, or Ancon, sheep 

 of North America was also the result of a sudden variation ; and 

 the differences in the form of its skeleton from that of the common 

 sheep amounted to a specific if not a generic difference." It 

 is true, as this writer says, these and other instances that could 

 be mentioned have arisen under domestication.^ But he per- 

 tinently asks why may not the same kind of thing be taking place 

 in the wild state ? " 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 we 

 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 last of its race." 



The instances just cited are cases in which new species have 

 suddenly appeared without known cause — no one has been able to 

 fix upon any external determining conditions. Other instances, 

 however, are known where, as with the famous metamorphosis of 

 the Axolotl, a more^or less definite and known change of conditions 

 has helped to bring about the transformations in question. 



One such case, where a marked alteration in climate was opera- 

 tive, has been cited by Darwin.3 Metzger obtained seeds of a 

 tall kind of maize {Zea altissima) from the warm regions of America 

 and cultivated them in Germany. During the first and second 

 years the plants reared showed some differences from the parent 

 stock, and, " In the third generation nearly all resemblance to the 

 original and very distinct American parent-form was lost. In the 

 sixth generation this maize perfectly resembled a European 

 variety. . . . When Metzger published his book, this variety was 



' " Habit and Intelligence," 1869, vol. i., p. 343. 



= " It is certain that the Ancon and Mauchamp breeds of sheep, and almost 

 certain that the Niata cattle, turnspit and pug-dogs, jumper and frizzled fowls, 

 short-faced tumbler pigeons, hook-billed ducks, &c., and with plants a multitude 

 of varieties, suddenly appeared in nearly the same state as we now see them " 

 (Darwin, loc. cit., vol. ii., p. 414). 



3 " Animals and Plants under Domestication," vol. i., p. 322. 



