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know that there is a single fact which can justify any 

 one in asserting that such sterility cannot be produced 

 by proper experimentation. For my own part, I see 

 every reason to believe that it may, and will be so pro- 

 duced. For, as Mr. Darwin has very properly urged, 

 when we consider the phenomena of sterility, we find 

 they are most capricious ; we do not know what it is 

 that the sterility depends on. There are some animals 

 which will not breed in captivity ; whether it arises 

 from the simple fact of their being shut up and deprived 

 of their liberty, or not, we do not know T , but they 

 certainly will not breed. What an astounding thing 

 this is, to find one of the most important of all functions 

 annihilated by mere imprisonment ! 



So, again, there are cases known of animals which 

 have been thought by naturalists to be undoubted spe- 

 cies, which have yielded fertile hybrids ; while there 

 are other species which present what everybody believes 

 to be varieties* which are more or less infertile with 

 one another. There are other cases which are truly 

 extraordinary ; there is one, for examjDle, which has 

 been carefully examined, — of two kinds of sea-w T eed, 

 of which the male element of the one, which we may 

 call A, fertilizes the female element of the other, B ; 

 while the male element of B will not fertilize the female 

 element of A ; so that, while the former experiment 

 seems to show us that they are varieties, the latter 

 leads to the conviction that they are species. 



* And as I conceive with very good reason ; but if any objec- 

 tor urges that we cannot prove that they have been produced by 

 artificial or natural selection, the objection must be admitted — 

 ultra-sceptical. as it is. But in science, scepticism is a duty. 



