238 



PRINCIPLES OF POULTRY BREEDING 



Variations in color are dependent upon quality and are based 

 upon certain chemical constituents in the feathers, or upon the 

 refraction and reflection of light due to the character of the surfaces. 

 Substantive variations are undoubtedly of the greatest service 

 in poultry breeding. They are closely associated with efficiency, 

 utility, color pattern, quality of flesh and bone, color of flesh 

 and skin. 



Meristic variation represents alternations in the form or in 

 the repetition of parts. It usually manifests itself by a departure 



from the normal systemat^ 

 ic or specific plan of the 

 birds. For example, the 

 normal chicken has two 

 legs; the addition of other 

 legs would constitute a 

 meristic variation in the 

 type (Fig. 122). Meristic 

 variations are of little eco- 

 nomic importance, as they 

 usually appear as abnor- 

 malities which have no 

 practical value. To the 

 student of biology they 

 open up a vast field concerning the real nature of livmg matter. 

 Functional variation relates to alteration in the normal activity 

 of the various organs or parts of the bird, such as rpdscular activity, 

 glandular secretions, and the like (Fig. 123). It has to do, not with 

 the form of the organs, but with their functions. The best examples 

 of functional variation are the individual variation in egg produc- 

 tion in females and the variation in the prepotency of males and 

 their power to fertilize a given number of eggs. Functional activi- 

 ties are influenced, and variations caused, by many factors, among 

 the more important of which are exercise, feed, improper environ- 

 ment, and care. All of these should be regulated by the careful 

 poultry breeder, if his efforts in mating and breeding are to be 

 followed by the fullest development and improvement. 



Mutations. — Mutations, as distinct from ordinary variations, 

 may be described as unlooked-for or accidental deviations from 

 type. The new type formed is not the result of slow continuous 

 selection and fluctuation, but, with no intermediate stage between 

 the old type and the new, there is a sudden change of form. Muta- 



-Chick with four legs— 

 meristic variation. 



an example of 



