THE LAW OF HEREDITY 83 



thoronglily understood. At present the materials for 

 a comprehensive judgment upon the subject are lack- 

 ing. Few of us know anything of the real character 

 of our grandfathers or grandmothers, and remoter 

 ancestors are quite beyond our ken. Even in the 

 case of illustrious men, the facts that would be most 

 useful to the student of heredity have not been ob- 

 served or recorded. From this point of view very 

 little existing biography is of any value. If anything 

 is told us of a great man's father, his mother is often 

 ignored altogether, and in any case the facts related 

 are usually meagre. It is certain that many of our 

 instincts are very deeply rooted. In menageries 

 straw that has served as litter in the lion's or the 

 timer's cage is useless for horses ; the smell of it terri- 

 fies them, although countless equine generations must 

 have passed since their ancestors had any cause to 

 fear attack from feline foes.^ 



By the seemingly capricious action of the germ- 

 plasm a curious element of uncertainty is introduced 

 into heredity. This is the tendency of characteristics 

 to become metamorphosed in passing from parent to 

 child. Nervous affections are especially subject to 

 this transformation. Convulsions in the parent may 



^ Laycock's Organic Laws of Fersoiial and Ancestral Memory, 



