THE STUDY OF INHERITANCE. 483 



arrest, but the view that it is due to some adverse circum- 

 stance which has kept the individual from completing its devel- 

 opment is much more simple and probable than the view that 

 the child inherits its distinct premaxilla from any ancestor 

 except its parents. 



When the son of a beardless boy grows up and acquires a 

 beard, we may be permitted to say that he has inherited his 

 grandfather's beard ; but this is only a figure of speech, and he ac- 

 tually inherits the beard which his father might have acquired 

 had he lived ; nor would the case of a child 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 were finally to put the last of the series where it did 

 flower, we should not be justified in saying that it did 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 in hydroids 

 present illustrations of the normal inheritance of latent charac- 

 ters, but we find in them no ground for the assertion that the 

 ancestral characteristics 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 statistical 

 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 natural group of ani- 

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

 the ratio between the lengths 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 existence of a stand- 

 ard, the mean or average, to which the majority adhere pretty 

 closely, while other members of the group are more abnormal, 

 and show marked deviation from the mean. 



If the cases tabulated are numerous enough, the individ- 

 uals will conform, so far as this quality is concerned, to what 

 is known in statistical science as the law of frequency of error. 

 This agreement will be so close, when great numbers of in- 

 stances are examined, that the number of individuals which 

 depart from the mean to any specified degree may be computed 

 mathematically. 



