190 THE MENDEL JOURNAL 



in some, but not all,* of the charts in his collec- 

 tion for twins to be produced in the later part of 

 married life, and the probability therefore exists that had 

 this woman had any further children some of them might 

 have been twins. A glance at the other twin-bearing 

 fraternities in this Chart enables us to consider this 

 probability. Among the children of Nos. 5 and 9, B 

 Generation, and of No. 1, D Generation, the twins were 

 produced at the fifth, fifth and seventh births respec- 

 tively. This clearly suggests that the woman No. 3, B. 

 Generation, who had eight children, and none of them 

 twins, did not carry the twin-producing capacity, and 

 therefore represents in respect of this quality a Men- 

 delian segregation from a twin-producing stock. The 

 evidence is not, of course, conclusive. But it is certainly 

 significant. 



The third feature of interest in this Pedigree is that 

 although, as I am informed by my medical colleagues at 

 the London Hospital, nephritis " is more common among 

 men than among women, on account of the greater ex- 

 posure to which thej^ are subjected," yet if we trace the 

 descent of it through the members of the Pedigree it will 

 be noticed that only females suffered from this disease or 

 from one of its manifestations, vesical calculi. Now we 

 may doubt whether mere exposure is sufficient by itself to 

 produce nephritis. Doubtless if the inherent tendency 

 to contract it is there, exposure will hasten or determine 

 its manifestation. But in this clanship the evidence 

 shows a definite hereditary tendency to acquire the 

 disease, which seems present in some and absent in others. 

 There is no reason, for instance, to believe that the woman 

 No. 1, C Generation, was less exposed in her life to con- 

 ditions supposed to be favourable to the production of 

 nephritis than her mother and one of her daughters, who 

 both contracted it. She herself apparently never suffered 

 from the disease, but nevertheless transmitted one of its 

 manifestations to one of her daughters. 



The fourth feature of interest is the large proportion 

 of females which this clanship produces. Out of a total 

 of thirty-nine people whose sex has been ascertained, 



* See for instance Pedigree B, where the earlier children are sometimes 

 twins. 



