LAW OF CORRELATION 241 
hen which was the female ancestor of the Barred Plymouth Rock 
breed. Atavism may be shown in form, color, or functional activi- 
ties. Its tendencies are of two kinds: 
1. Those characteristics which are apparently lost but which 
crop out in pure birds after many years or generations of straight 
breeding. 
2. Those outcropping characteristics which appear in the 
descendants of crossbred birds, and which have not previously 
shown themselves in any descendants of the cross or which soon 
disappeared after the original cross. 
The prevalence of either of these tendencies is governed or 
largely influenced by the following factors: 
1. The degree of purity, or the time elapsed since pure breed- 
ing was begun. The more generations there have been of pure 
breeding, the less likelihood is there of reversion to show. 
2. The purity of breeding of either parent when new blood is 
introduced for desired vigor and vitality. It is safest practice to 
do one’s own breeding so far as possible, as when purchasing alien 
males there can be no certainty of their purity with respect to 
certain desirable traits. 
3. Lack of prepotency in either or both parents permits rever- 
sion to crop out, because they lack the power to subdue latent 
characteristics. 
The results which atavism may accomplish are of no practical 
value to the breeder. But a knowledge of its workings convinces 
him of the folly of using grade sires of unknown ancestry in breed- 
ing for either eggs or meat purposes, also that to produce definite 
results and to develop a pure line of standard-bred poultry he 
must avoid crossing. 
Law of Correlation.— By correlation is meant the relation which 
exists between the form and functions of various organs of the 
bird’s body. Correlation exists between all forms of animal life 
and makes possible their systematic classification. 
Poultry offers an exceptionally fertile field for the study of 
correlated features, as they have many variable and easily defined 
parts. Some of the following are especially interesting correl- 
atives. The form and size of the individual is often proportional 
to the form and size of its parts. For example, a bird with a long 
neck is very apt to be “ rangy ” throughout, with long body, legs, 
and head. The reverse is also true, and a bird with short, compact 
body and neck usually has short, stout legs, back, and head. 
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