VII ON THE INFERTILITY OF CROSSES 163 



163) was the first to mention, I believe, that in different parts 

 of South America the ram is more usually crossed with the 

 she-goat than the sheep with the he-goat. The well-known 

 'pellones' of Chile are produced by the second and third 

 generation of such hybrids (Gay, ' Hist, de Chile,' vol. i. p. 466, 

 Agriculture, 1862). Hybrids bred from goat and sheep are 

 called 'chabin' in French, and 'cabruno' in Spanish. In 

 Chile such hybrids are called 'carneros lanudos'; their breed- 

 ing inter se appears to be not always successful, and often the 

 original cross has to be recommenced to obtain the proportion of 

 three-eighths of he-goat and five-eighths of sheep, or of three- 

 eighths of ram and five-eighths of she-goat ; such being the 

 reputed best hybrids." 



With these numerous facts recorded by competent observers 

 we can hardly doubt that races of hybrids between these very 

 distinct species have been produced, and that such hybrids are 

 fairly fertile inter se; and the analogous facts already given lead 

 us to believe that whatever amount of infertility may at first 

 exist could be eliminated by careful selection, if the crossed 

 races were bred in large numbers and over a considerable area 

 of country. This case is especially valuable, as showing how 

 careful we should be in assuming the infertility of hybrids 

 when experiments have been made with the progeny of a single 

 pair, and have been continued only for one or two generations. 



Among insects one case only appears to have been recorded. 

 The hybrids of two moths (Bombyx cynthia and B. arrindia) 

 were proved in Paris, according to M. Quatrefages, to be fertile 

 inter se for eight generations. 



Fertility of Hybrids among Plants. 



Among plants the cases of fertile hybrids are more numerous, 

 owing, in part, to the large scale on which they are grown by 

 gardeners and nurserymen, and to the greater facility with 

 which experiments can be made. Darwin tells us that Kolreuter 

 found ten cases in which two plants considered by botanists 

 to be distinct species were quite fertile together, and he there- 

 fore ranked them all as varieties of each other. In some 

 cases these were grown for six to ten successive generations, but 

 after a time the fertility decreased, as we saw to be the case in 



