RELATION TO GENERAL BIOLOGICAL I'RGiiLLALS 123 



is statisticaL Danforth' in a popular article conccrninj^ 

 the heredity of twinning has collected data that may 

 readily be interpreted as indicating that the tendency 

 is not merely sporadic, but has a congenital basis. 

 Fifty pairs of newborn twins were found to have 171 

 singly born and 10 twin older brothers and sisters, 

 a ratio of 1:18. In mothers' fraternities (i.e., bro- 

 thers and sisters) there were 318 single births and ten 

 pairs of twins (1:32), and in fathers' fraternities 219 

 single and eight pairs of twins (1:37). When these 

 ratios are compared with the normal incidence of twins 

 (1:90.6), it appears that certain strains are more 

 hable to twins than others; this implies a hereditary 

 tendency. 



I am well acquainted with a family in which strik- 

 ingly similar duplicate twins occurred in two con- 

 secutive births. The first pair were females, the second 

 pair males. A collection of data of this sort would be 

 very interesting, as it would tend to indicate that 

 monozygotic twinning is hereditary-; no other such 

 data are available to me. 



Whether the tendency to twinning is a factor resident 

 in the mother or the father is not clear. That the 

 twinning factor, whatever it may be, might reside in 

 the father is suggested by an extraordinary case cited 

 by R. Berger.^ The case concerns a man whose tirst 

 wife had quadruplets once and twins ten times; his 

 second wife had triplets three times and twins ten 

 times. The man was the father of sixty-eight children. 

 Dr. Berger inferred that the tendency to twinning is 



'C. H. Baniorth, Journal of Heredity, VII (1916)- 

 ^ Zentralblatt f. Gyndkologie, X (1914). 



