THE INHERITANCE OP FAMILY TRAITS 12a 



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 



DiO 



^iMiXi 



• ■ □ O 



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

 symbols. F. R. 



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

 then, normal daughters in a myopic fraternity may expect 

 nyopic sons. 



p. Astigmatism. — This condition of improper curvature 

 of the lens belongs to the Hst 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 

 3e desirable, other things being equal, for a person belonging 

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

 las normal eyes. 



28. Ear Defects 



The ear is the most complicated of the sense organs and 

 ;hough its important elements are deeply hidden in the 

 lead yet the lining of the middle ear is continuous with the 



