breeder in Kincardineshire. He bought a black bull, the son of a black cow
with white legs, white belly and part of the tail white; and in 1870 a calf
the gr.-gr.-gr.-gr.-grandchild of this cow was born coloured in the same very
peculiar manner; all the intermediate offspring having been black. In these
cases there can hardly be a doubt that a character derived from a cross with
an individual of the same variety reappeared after passing over three
generations in the one case, and five in the other.

When two distinct races are crossed, it is notorious that the tendency in the
offspring to revert to one or both parent-forms is strong, and endures for
many generations. I have myself seen the clearest evidence of this in crossed
pigeons and with various plants. Mr. Sidney (13/17. In his edition of 'Youatt
on the Pig' 1860 page 27.) states that, in a litter of Essex pigs, two young
ones appeared which were the image of the Berkshire boar that had been used
twenty-eight years before in giving size and constitution to the breed. I
observed in the farmyard at Betley Hall some fowls showing a strong likeness
to the Malay breed, and was told by Mr. Tollet that he had forty years before
crossed his birds with Malays; and that, though he had at first attempted to
get rid of this strain, he had subsequently given up the attempt in despair,
as the Malay character would reappear.

This strong tendency in crossed breeds to revert has given rise to endless
discussions in how many generations after a single cross, either with a
distinct breed or merely with an inferior animal, the breed may be considered
as pure, and free from all danger of reversion. No one supposes that less than
three generations suffices, and most breeders think that six, seven, or eight
are necessary, and some go to still greater lengths. (13/18. Dr. P. Lucas,
'Hered. Nat.' tome 2 pages 314, 892: see a good practical article on the
subject in 'Gardener's Chronicle' 1856 page 620. I could add a vast number of
references, but they would be superfluous.) But neither in the case of a breed