HY BRIDOUS 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 strue- 
ture and instincts. ‘ If it be true,” (says J. Hunrer, 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 i 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 hkewise in the produc- 
tion of mules, so that sometimes a mule shall breed, from 
the circumstance of its bemg a monster respecting mules * ?” 
Whenever we observe animals in a free state, and where 
there is room for choice, engaging willingly m the business 

* Phil. Trans. 1787, p. 253. 
