14 VARIATION UNDER DOMESTICATION. [Chap. I 



of the " crackers " {i.e. Virginia squatters) added, " we 

 select the black members of a litter for raising, as they 

 alone have a good chance of living." Hairless dogs have 

 imperfect teeth; long-haired and coarse-haired animals 

 are apt to have, as is asserted, long or many horns; 

 pigeons with feathered feet have skin between their 

 outer toes; pigeons with short beaks have small feet, 

 and those with long beaks large feet.J^Hence if man 

 goes on selecting, and thus augmenting, any peculiarity, 

 he will almost certainly modify unintentionally other 

 parts of the structure, owing to the mysterious laws of 

 correlation. 



The results of the various, unknown, or but dimly 

 understood laws of variation are infinitely complex and 

 diversified. It is well worth while carefully to study 

 the several treatises on some of our old cultivated 

 plants, as on the hyacinth, potato, even the dahlia, &c.; 

 and it is really surprising to note the endless points of 

 structure and constitution in which the varieties and 

 sub-varieties differ slightly from each other. The 

 whole organisation seems to have become plastic, and 

 departs in a slight degree from that of the parental 

 type. 



Any variation which is not inherited is unimportant 

 for us. But the number and diversity of inheritable 

 deviations of structure, both those of slight and those of 

 considerable physiological importance, are endless. Dr. 

 Prosper Lucas's treatise, in two large volumes, is the 

 fullest and the best on this subject. No breeder doubts 

 how strong is the tendency to inheritance; that like 

 produces like is his fundamental belief: doubts have 

 been thrown on this principle only by theoretical 

 writers. When any deviation of structure often appears, 



