128 MARRIAGE AND HEREDITY 



imagination continues to be very prevalent at the 

 present day. But it is erroneous. It did not even 

 accord with the facts ascertained in Goethe's time, for 

 the manifestation of heredity by influence, as this 

 class of phenomena is somewhat ineptly called, is 

 frequent in the case of certain of the lower animals, 

 such as pigs, which are not supposed to be governed 

 by imagination. A domestic sow having bred once 

 with a wild boar, or a boar of a particular breed, con- 

 tinues in subsequent litters to produce young exhibit- 

 ing a greater or less admixture of the strange blood. 

 Breeders of animals are well aware of the danger 

 caused to the purity of a stock by a single case of 

 promiscuous crossing. No work on breeding is com- 

 plete without a reference to the famous quagga colts. 

 An English mare was crossed in 1815 by a quagga, 

 a spotted ass of Africa. The mule so bred was spotted 

 like its father. Its parents were never again brought 

 together. In 1817, 1818, and 1823 the same mare 

 was crossed by Arab stallions, and in each case she 

 produced a colt spotted like the quagga. Breeders 

 have never forgotten this case, which was an epoch- 

 maldng one in their craft. For a long time they were 

 unable to explain it. Darwin, however, discovered 

 the key to the mystery in studyins the fertilisation 



