THE INHERITANCE OF FAMILY TRAITS 109 



in this inhibitor; the affected female is typically duplex, 

 rarely simplex; unaffected males are always nulliplex, and 

 unaffected females are either nulliplex or simplex. 



The eugenic conclusion is: No female with the coloboma 

 defect shoidd have children since all sons will be defective 

 in the structure of the pupil. For males with the defect the 

 danger in marriage is also great, for either all or half of the 



S4i 



6N 



Fig. 75. — ^This is the pedigree of a family (Payne) with coloboma of the 

 iris. I, 1, and 2 are not definitely known; at least 1 of their sons and 4 daugh- 

 ters are affected. As for the rest, two normal parents have normal offspring. 

 The apparent exception, V, 2, may not be such as the mother, IV, 2, is wholly 

 unknown. The number of affected females in this pedigree is extraordinary. 

 Debeck, 1886. 



sons of such a father, although married to a woman from a 

 normal strain, will be defective, but the daughters will not 

 be defective in this respect unless the wife belongs to a strain 

 with this defect. Two normal persons may marry with 

 impimity except that if the woman belongs to the abnormal 

 strain it may be that haK of her sons will be affected. 



b. Reduction in size of the Eyeball. — All grades in the 

 size of the eyeball down to complete disappearance are 

 known, but usually only the extremely reduced condition 

 has been studied. Such a condition seems to be due to an 

 inhibitor so that, when present in a marked degree, all off- 

 spring shall have it. Both sexes seem to be equally affected. 



