LAW OF CORRELATION 241 



hen which was the female ancestor of the Barred Plymouth Rock 

 breed. Atavism may be sho^\^l 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 

 largel}^ 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 ovm. 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. 



16 



