46 THE ORIGIN OF SPECIES 



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in the great majority of cases, this touchstone for 

 species is wholly inapplicable. 



The constitution of many wild animals is so 

 altered by confinement that they will not breed 

 even with their own females, so that the negative 

 results obtained from crosses are of no value ; and 

 the antipathy of wild animals of different species 

 for one another, or even of wild and tame members 

 of the same species, is ordinarily so great, that it 

 is hopeless to look for such unions in Nature. 

 The hermaphrodism of most plants, the difficulty 

 in the way of insuring the absence of their own 

 or the proper working of other pollen, are obsta- 

 cles of no less magnitude in applying the test to 

 them. And, in both animals and plants, is super- 

 added the further difficulty, that experiments 

 must be continued over a long time for the purpose 

 of ascertaining the fertility of the mongrel or 

 hybrid progeny, as well as of the first crosses from 

 which they spring. 



Not only do these great practical difficulties lie 

 in the way of applying the hybridisation test, but 

 even wlien this oracle can be questioned, its replies 

 are sometimes as doubtful as those of Delphi. 

 For example, cases are cited by Mr. Darwin, of 

 plants which are more fertile with the pollen of 

 another species than with their own ; and there 

 are others, such as certain Fuci, the male element 

 of which will fertilise the ovule of a plant of 

 distinct species, while the males of the latter 



