THE INHERITANCE OF FAMILY TRAITS 123 



controlled by heredity has been shown by Hertel (1903), 

 as a result of measuring the refraction in children and their 

 parents. 



That myopia, or near sightedness, is inheritable has long 

 been known, A typical case has been recorded by Oswald 

 (1911), Fig. 90, and a second pedigree is given by Worth 

 (Fig. 91). In both pedigrees inheritance is sex-limited as in 

 color blindness. A normal female has some, at least, of her 



DtO 



4"^JMMJi6i 



iT^ 



Fig. 92. — Pedigree of astigmatism, affected persons represented by black 

 symbols. F. 'R. 



sons myopic, but all daughters are normal. In such a family, 

 then, normal daughters in a myopic fraternity may expect 

 myopic sons. 



p. Astigmatism. — This condition of improper curvature 

 of the lens belongs to the list of family traits. A corre- 

 spondent submits the pedigree of his family shown in Fig. 92. 



From this pedigree it appears that, in this family, astigma- 

 tism is a recessive trait, since normal persons may transmit 

 it and since it is equally apt to appear in either sex. It would 

 be desirable, other things being equal, for a person belonging 

 to an affected strain to seek a partner from a strain that 

 has normal eyes. 



28. Ear Defects 



The ear is the most complicated of the sense organs and 

 though its important elements are deeply hidden in the 

 head yet the Uning of the middle ear is continuous with the 



