10 Heredity. 



unorganized ^gg, of a power to produce a definite adult 

 animal, with all its characteristics, even down to the 

 slightest accidental peculiarity of its parents; a power 

 to reproduce in it all their habits and instincts, and even 

 the slightest trick of speech or action. 

 . This is by no means the whole of the problem of he- 

 redity. One of tlie most interesting phenomena con- 

 nected with our subject is what is known as reyersion, 

 or the appearance in the child of peculiarities which 

 were not joresent in either parent, but are due to inheri- 

 tance from a grandparent or a more remote ancestor. 

 An interesting illustration of this law is the occasional 

 appearance in horses of stripes on tlie body and legs. 

 Such stripes are not usually present in the horse, al- 

 though Darwin has given reasons for believing that our 

 horses are descended from a striped zebra-like ancestor. 

 The power to revert to this ancestral form is handed 

 down from generation to generation in the Qgg, and it 

 may show itself at any time by the production of a 

 striped colt. Eeversion is, in a certain sense, exception- 

 al, but it is not at all rare, and we must add tins power 

 to the wonderful properties of the ^gg. 



Darwin gives the following case, which will serve to 

 illustrate the nature of reversion: A pointer bitch pro- 

 duced some puppies; four were marked with blue and 

 white, which is so unusual a color in pointers that she 

 was thought to have played false with one of the grey- 

 hounds, and the whole litter was condemned, but the 

 gamekeeper was permitted to save one as a curiosity. 

 Two years afterwards a friend of the owner saw the 

 young dog, and declared that he was the image of his old 

 pointer bitch, Sappho, the only blue and wdiite pointer 

 of pure descent which he had ever seen. This led to 

 close inquiry, and it was proved that he was the great- 



