18 FARM ANIMALS 
them to the old heredity, and builds or improves the 
structure to higher and better ends. 
The breeder’s work is to fix the new acquisitions and to make 
them a part of the building material; and all the while he allows 
variation free range that it may gather in new discoveries for fur- 
ther improvement and use. When found, through the law of hered- 
ity, they are transmitted to the betterment of the class or breed. 
In improving a herd or flock it is part of the breeder's work to 
decide which of the new things that variation has found shall be 
held, which shall be cast aside, and at what point a new acquisition 
is to be fixed as a part of the old stock. In this way improvement 
is secured through heredity, variation and selection. 
STRIKING VARIATION IN FOWLS 
These breeds have been evolved from a single ancestry. A, Houdan; b, English 
Game; c, Barred Plymouth Rock; d, White Polish; e, Japanese Bantam; f, Light 
Brahma; g, Aseel; h, Ceylon jungle fowl; i, White Wyandotte. 
10. Atavism.—Often it is observed that there is a re- 
appearance of peculiarities or traits after a lapse of one 
or more generations, either in the lower animals or in 
man. This phenomenon is known as atavism, or “breed- 
ing back.” It is simply a reoccurrence to the surface of 
some old trait that had supposedly become eliminated. 
11. Crossing peas.——Gregor Johann Mendel, an Aus- 
trian monk, conducted many experiments with peas. In 
crossing different varieties, and subsequently planting 
their offspring, he observed the inheritance of contrasting 
characters in the hybrids or crosses. He made crosses 
(hybrids he called them) between varieties which differed 
markedly as regards a pair or several pairs of characters, 
