An Introduction to a Biology 



rose-combed birds. The general conclusion derived from 

 cases such as this is one of the utmost importance in prac- 

 tical breeding. It is that the appearance of the individual 

 furnishes no clue as to its breeding properties ; and its 

 ancestry helps just as little. Both the pure and hybrid 

 tails of the second hybrid generation had precisely the same 

 ancestry ; and yet the pure produces only tails, and the 

 hybrid produces dwarfs as well. The individual itself can 

 tell us nothing of its breeding properties ; nor can its an- 

 cestry. To know how a given animal will breed, we must 

 breed from it and see. Once we have found that its " get " 

 is good we may be confident that the rest of its offspring will 

 be up to the same standard. To estimate the breeding 

 properties of a given animal we must not look straight in 

 front of us at the animal himself ; we must not look back, 

 through its pedigree, at its ancestors ; all we need to do is 

 to look forward a little way, one generation in fact, at a fair 

 sample of its progeny. This is indeed the lesson which I 

 wish to drive home in this article. And I shall return to 

 it again when more of the facts have been considered. 



We will now take a brief glance at one of the first and 

 most striking extensions of Mendel's rules from the vegetable 

 to the animal kingdom. This is the classical case of the Anda- 

 lusian fowl. It is a useful case, because it enables us to see in 

 striking contrast the difference between the Mendelian rules 

 of breeding and the older rules which the Mendelian rules bid 

 fair to supplant. The blue Andalusian fowl is characterised 

 by a beautiful slaty-blue plumage, each feather edged, or 

 " laced " as it is called, with a darker tinge of the same 

 colour. If you buy a pen of these blue Andalusians and hatch 

 the eggs, you will be disappointed to find that only about 

 hatf the chicks are like their parents ; the remaining half 

 will consist of black birds and white birds with occasional 

 blackish feathers. You will probably put this impure breed- 

 ing down to some recent cross amongst the ancestors of 

 the birds you bought, and proceed to breed from the blue 



