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- 
SU Ss malities which have no 
Fie. 122.—Chick with four legs—an example of practical value. To the 
meristic variation. student of biology they 
open up a vast field concerning the real nature of living matter. 
Functional variation relates to alteration in the normal activity 
of the various organs or parts of the bird, such as muscular 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- 
