LECTURE XIV. 415 



present some wolf-character, just as a race-horse may show 

 zebra stripes about the feet ; but, generally speaking, the 

 hybrid race disappears, and is absorbed in the original stock. 



Experience now teaches that fertility among hybrids differs 

 in a remai'kable degree ; that each species has its own law ; 

 that there obtains even a difference with regard to the sexes of 

 the same species. The he-goat pairs readily with the sheep, 

 and produces hybrids which, according to Buffon, are per- 

 fectly prolific. The ram, on the other hand, copulates unwill- 

 ingly with the goat ; and, according to the same naturalist, 

 there never is any issue. The probable production of prolific 

 young, as Broca justly observes, by no means depends on the 

 external resemblance of characters. 



The greyhound and poodle dog are, both externally as well 

 as in the structure of the bones, much more dissimilar than 

 horse and ass (though greyhound and poodle are considered 

 races of the same species, but horse and ass as different spe- 

 cies), and yet the former produce fertile, and the latter a sterile 

 progeny. Observation alone can furnish us with data; and obser- 

 vation, we must confess, extends at present to but few species. 



There are cases in which the sexual function of hybrids is 

 extremely limited^ in which the bastards may copulate, but are 

 sterile. Mules may sometimes produce young, but they must 

 be covered by a horse stallion, and the progeny are usually 

 sterile, and possess little viability. This example, which is 

 the oldest and best known, is the only one, and may be consi- 

 dered as exceptional. Mule breeding has been carried on in 

 the East from the remotest antiquity, and it was reserved to 

 the enlightened government of King Otho of Greece to ignore 

 a thousand years'" experience, and to import from Portugal, at 

 a great expense, mule stallions for the improvement of mule 

 breeding in Greece. This example of stei'ile hybrids is con- 

 stantly quoted by those who maintain " all hybrids are gene- 

 rally sterile in the first or the next following generations." 



Broca cites an instance of a limited hybrid production be- 

 tween the American bison and the European cow. The bison 

 readily covers the cow, whilst the domestic bull manifests an 

 aversion to the bison-cow. The progeny from such a connec- 



