102 DOMESTICATED ANIMALS AND PLANTS 
correlation is said to be negative. In general, while characters 
are more or less indifferent to each other, there is, for the most 
part, a low but real correlation. Methods of calculating this cor- 
relation are well known and are extensively used in statistical 
studies, but are rather too complicated for introduction here (see 
reference to “ Principles of Breeding ” just given). 
Fic. 16. Albino deer. Specimen owned by State Museum, Augusta, Maine 
Lost characters. In the vicissitudes of time and selection 
characters are sometimes lost. Thus the whale, which is a true 
mammal, like the cow, and which once lived upon the land, has 
lost its hind legs except for a few pelvic bones. Birds have lost 
one ovary. The whole snake family has lost one lung, and all 
but the python have lost all traces of their legs. 
Some colors are the result of pigment formation. This quality 
is often lost, resulting sometimes in an albino individual, as in 
