156 THE FOUNDATIONS OF ZOOLOGY 



same result. We do not know what arrested development, but 

 the view that this was some adverse circumstance in the history 

 of the individual is surely more simple than the opinion that the 

 child inherits its distinct premaxilla from any ancestor except its 

 parent. The same thing is true of the polydactylism of horses, 

 although this is sometimes attributed to reversion to miocene 

 ancestors. 



When the son of a beardless boy and a beardless woman 

 grows up and acquires a beard, we may be permitted to say he 

 has inherited his grandfather's beard ; but this is only a figure 

 of speech, for he actually acquires nothing except what was latent 

 in his parents ; nor would the case of a bearded man descended 

 from a series of ten or a hundred beardless boys and beardless 

 women be any different. If we were to propagate a plant by 

 cuttings for ten or a hundred generations under conditions which 

 did not permit it to flower, and if, finally, we put the last where 

 it does flower, we should not be justified in saying that it does 

 not inherit its flower from the preceding cutting ; nor would the 

 case be any different if, for some reason, this preceding cutting 

 could not be made to bloom. 



The phenomena of polymorphism in insects and hydroids 

 present illustrations of the normal inheritance of latent characters, 

 but we find in them no ground for the assertion that the ances- 

 tral characters of the medusa are not inherited from the hydroid 

 which produces it. 



The sum of the visible features of the parent, plus the sum 

 of its latent potencies, may be called a " mid-parent " for statis- 

 tical purposes, if we see fit, but there is no evidence that this 

 " mid-parent " is anything else than the actual parent. 



With this introductory note, we may now enter upon the 

 study of Galton's works, the central point of which is as follows : 

 If we select any one characteristic of a group of animals, — 

 such a characteristic as the weight of the individuals, or the 

 ratio between the length of their arms and legs, or anything 

 else which admits of exact numerical statement, — it will be 

 found that, while no two members of the group are exactly 

 alike, they nevertheless conform to a type, and show the exis- 

 tence of a standard, the mean or average, to which the majority 



