HYBRIDOUS ANIMALS. 431 



3. The Hybridous Products are barren. The peculiar 

 circumstances which are required to bring about a sexual 

 union between individuals of different species, sufficiently 

 account for the total absence of hybridous productions in a 

 wild state. And, as if to preserve even in a domesticated 

 state the introduction and extension of spurious breeds, 

 such hybridous animals, though in many cases disposed to 

 sexual union, are incapable of breeding. There are, in- 

 deed, some statements which render it probable that hybrid 

 animals have procreated with perfect ones ; at the same 

 time there are few which are above suspicion. Where such 

 occurrences have taken place, and they are unquestionably 

 very rare, the species have been very closely allied in struc- 

 ture and instincts. " If it be true," (says J. HUNTER, with 

 great plausibility,) " that the mule has been known to breed, 

 which must be allowed to be an extraordinary fact, it will 

 by no means be sufficient to determine the Horse and Ass 

 to be of the same species : indeed, from the copulation of 

 mules being very frequent, and the circumstance of their 

 breeding very rare, I should rather attribute it to a degree 

 of monstrosity in the organs of the mule which conceived ; 

 not being those of a mixed animal, but those of the mare 

 or female ass. This is not so far fetched an idea, when we 

 consider that some true species produce monsters, which 

 are a mixture of both sexes, and that many animals of dis- 

 tinct sex are incapable of breeding at all." " If, then, we 

 find Nature in its greatest perfection deviating from general 

 principles, why may not it happen likewise in the produc- 

 tion of mules, so that sometimes a mule shall breed, from 

 the circumstance of its being a monster respecting mules * ?" 

 Whenever we observe animals in a free state, and where 

 there is room for choice, engaging willingly in the business 



* Phil. Trans. 1787, p. 253. 



