DEGREES OF STERILITY. 283 



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 onposition to the constantly repeated admon- 

 ition 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-authen- 

 ticated cases of perfectly fertile hybrid animals, I have 

 reason to believe that the hybrids from Cervulus vaginalis 

 and Reevesii, and from Phasianus colchicus with P. tor- 

 quatus, are perfectly fertile. M. Quatrefages states that 

 the hybrids from two moths (Bombyx cynthia and arrindia) 

 were proved in Paris to be fertile inter se for eight genera- 

 tions. 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 bred 

 inter se. This was effected by Mr. Eyton, who raised two 

 hybrids from the same parents, but from different hatches; 

 and from these two birds he raised no less than eight 

 hybrids (grandchildren of the pure geese) from one nest. 

 In India, however, these cross-bred geese must be far more 

 fertile; for I am assured by two eminently capable judges, 

 namely Mr. Blyth and Captain Hutton, that whole flocks 

 of these crossed geese are kept in various parts of the coun- 

 try; and as they are kept for profit, where neither pure 

 parent-species exists, they must certainly be highly or per- 

 fectly fertile. 



With our domesticated animals, the various races when 

 crossed together are quite fertile; yet in many cases they 

 are descended from two or more wild species. From this 



