28 



GUNNAR DAHLBERG 



Cases of more Hum one ehild ot <t birth in Stuttgart 

 and 4 additional villages. 



the one twin is determined quite irrespective of that of the other one, 

 and that chances are equal for its being a boy or a girl. In, such 

 a case the number of pairs of different sexes (made up of a boy and a 

 girl) and the number of pairs having the same sex (two boys or two girls) 

 ought to equal each other. If now the number of the two-sexed pairs 

 in a certain collection of twin material is known this figure has only 

 to be doubled to give the whole number of twins born from two ova. 

 If, on the other hand, this figure is subtracted from the total number 

 of twins, the remaining number must represent the number of twins 

 born trom one ovum. 



The method has been criticized by several workers (Ahlfeld etc.), 

 ])ut on the whole, Weinberg has been able to defend it successfully. 

 It is peculiar to find the Weinberg method so little known in the 

 English-speaking world. Margaret W. Cobb published a work, as 

 late as 1915, on the same method, evidently without having any know- 

 legde of Weinberg's work, and used it to determine the number of 

 births from one ovum in Connecticut, etc. 



However, let us return to the al)Ove table. Weinberg finds that 

 among the nearest relatives of the mothers producing twins from two 

 ova twin-births occur in the ratio of 1 : 44. Among the rest of the 

 population in this district (Stuttgart with 4 villages) the ratio of twin- 

 births is 1 : 92. Thus among the relations of the mothers of these 

 twins tw^in-birth appears about twice as often as among the rest of 

 the population; this speaks in favour of the view that the capacity of 

 giving birth to twins from two ova is inherited. 



