Chap. IX.] DEGREES OP STEBILITY. 9 



confinement, few experiments have been fairly tried: for 

 instance, the canary-bird has been crossed with nine dis- 

 tinct 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 in- 

 stance 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 con- 

 stantly 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 increas- 

 ing. 



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 (Bombyx cyn- 

 thia 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 off- 

 spring, 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 bred int$r 



