Chap. IX.] DEGEEES OF STEKILITY. 9 



breeding freely under confinement, few experiments 

 have been fairly tried : for instance, the canary-bird has 

 been crossed with nine distinct species of finches, but, 

 as not one of these breeds freely in confinement, we 

 have no right to expect that the first crosses between 

 them and the canary, or that their hybrids, should be 

 perfectly fertile. Again, with respect to the fertility 

 in successive generations of the more fertile hybrid 

 animals, I hardly know of an instance in which two 

 families of the same hybrid have been raised at the 

 same time from different parents, so as to avoid the ill 

 effects of close interbreeding. On the contrary, brothers 

 and sisters have usually been crossed in each successive 

 generation, in opposition to the constantly repeated 

 admonition of every breeder. And in this case, it is 

 not at all surprising that the inherent sterility in the 

 hybrids should have gone on increasing. 



Although I know of hardly any thoroughly well- 

 authenticated cases of perfectly fertile hybrid animals, I 

 have reason to believe that the hybrids from Cervulus 

 vaginalis and Eeevesii, and from Phasianus colchicus 

 with P. torquatus, are perfectly fertile. M. Quatrefages 

 states that the hybrids from two moths (Boiabyx 

 cynthia and arrindia) were proved in Paris to be fertile 

 inter se for eight generations. It has lately been 

 asserted that two such distinct species as the hare and 

 rabbit, when they can be got to breed together, produce 

 offspring, which are highly fertile when crossed with 

 one of the parent-species. The hybrids from the 

 common and Chinese geese (A. cygnoides), species 

 which are so different that they are generally ranked in 

 distinct genera, have often bred in this country with 

 either pure parent, and in one single instance they have 



