38 EVOLUTION OF TO-DAY. 



snake, between two genera, was born in the Zoologi- 

 cal Gardens of London. Hybrid ducks are common 

 and hybrid fishes are easily produced. In most of 

 these cases the hybrids thus produced are them- 

 selves sterile. But this is not true of all. The 

 cross between the rabbit and the hare, two good 

 species, is perfectly fertile. The cross between the 

 dog and the jackal, or the dog and the wolf or fox, 

 remains fertile, for a number of generations at least. 

 The common goose and the Chinese goose when 

 crossed produce perfectly fertile offspring ; and hy- 

 brids between the mallard and muscovy ducks show 

 no sterility. Infertility of hybrids is by no means a 

 universal law, among domestic species at all events. 

 But a similar hybridity has been observed among 

 animals in a state of nature. A cat has been de- 

 scribed by Cuvier, which is a cross between the do- 

 mestic cat and Felis Bangalensis. A hybrid duck is 

 known to exist in nature, and no less than eight 

 hybrid fresh-water fishes are known in Germany. 

 The polecat and the ferret produce hybrids. A male 

 white cockatoo and a female rose-colored cockatoo, 

 which never bred in confinement, were set at liberty 

 in the woods, and bred together for two years. It 

 is, of course, impossible to say whether hybrids are 

 themselves fertile or not, for no observations are 

 possible. 



A careful examination of the facts of cross-breed- 

 ing, collected by our ablest experimenters, reveals 

 thus several significant facts. It is true that in a 

 great majority of cases a certain amount of sterility 

 results from the crossing of distinct species. But 



