66 Heredity and Environment 



eral use the word "inheritance" refers to the repetition in suc- 

 cessive generations of such individual peculiarities. Among such 

 individual characters are the following: 



(a) Morphological Features. -Hereditary resemblances are 

 especially recognizable in the gross and minute anatomy of every 

 organism, in the form, structure, location, size, color, etc., of 

 each and every part. The number of such individual peculiarities 

 which are inherited is innumerable and only a few of the more 

 striking of these can be mentioned. 



It is a matter of common knowledge that unusually great or 

 small stature runs in certain families, and Galton developed a 

 formula for determining the approximate stature of children from 

 the known stature of the parents and from the mean stature' of 

 the race (Fig. 25). However, his statistical and mathematical 

 formulae give only general or average results, from which there 

 are many individual departures and exceptions. 



In the same way the color of the skin, the color and form of 

 hair and the color of eyes are in general like those of one or 

 more of the parents or grandparents. We all know that certain 

 facial features such as the shape and size of eyes, nose, mouth 

 and chin are generally characteristic of certain families. 



But the inheritance of anatomical features extends to much 

 more minute characters than those just mentioned. In certain 

 families a few hairs in the eyebrows are longer than the others, 

 or there may be patches of parti-colored hair over the scalp, or 

 dimples in the cheek, chin, or other parts of the skin may 

 occur, and these trifling peculiarities are inherited with all the 

 tenacity shown in the transmission of more important characters. 

 Johannsen has found races of beans in which the average weight 

 of individual seeds differed only by .02 to .03 gram, and yet these 

 minute differences in weight were characteristic of each race and 

 were of course inherited. Jennings has found races of Parame- 

 cium which show hereditary differences of .005 mm. in average 

 length (Fig. 22). Nettleship says that the lens of the human eye 



