SPECIES IN DOMESTIC BIRDS 29 



there are six color-varieties white, blue, black, red, yellow, and 

 silver. Birds of the same breed (shape) and the same variety 

 (color) may differ in some other character, as the form of the 

 comb or the presence or absence of feathers in certain places. 

 In accordance with such differences varieties are divided into 

 subvarieties. Thus, in Leghorn Fowls the brown, white, and buff 

 varieties have single-combed and rose-combed subvarieties. 



In any breed, variety, or subvariety certain families are some- 

 times distinguished for general or special excellence of form or 

 color. Such a family is called a strain. 



Systematic mixtures of breeds and varieties. Although so 

 many distinct varieties have been developed from common do- 

 mestic stocks, the improved races do not always displace the 

 mongrels. When the old mongrels disappear their place is often 

 taken by a new mongrel stock produced by mixtures of the dis- 

 tinct breeds with each other and with the old mongrel race. The 

 greater part of such stock is so mixed that its relation to any es- 

 tablished breed could not be determined or expressed, but sys- 

 tematic mixtures are sometimes made, and to describe these the 

 following terms are used : Crossbred having parents of differ- 

 ent, distinct breeds, varieties, or subvarieties. A Leghorn male 

 mated with a Cochin female produces offspring each of which 

 is in blood one half Leghorn and one half Cochin. Grade 

 having more than half of the blood of a breed. 



If the offspring of a cross such as is described in the preced- 

 ing paragraph are mated with birds of one of the parent breeds, 

 the offspring of this mating will have three fourths of the blood 

 of that breed. If these in turn are mated to birds of the same 

 pure breed, the offspring will have seven eighths of the blood of 

 that breed. Animals bred in this way are called grades until the 

 process has been carried so far that they are practically pure-bred. 

 Mongrel stock is often graded up in this way. As a rule stock 

 that is seven eighths pure is not distinguishable from average 

 pure stock of the same breed. 



