I02 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). 



Fig. 1 6. 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 



