142 mr. dakwin's woek and 



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, 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' 55 ' which are more or less infertile with 

 one another. There are other cases which are truly 

 extraordinary ; there is one, for example, 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 w r ill 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. 



