TWINS AND HEKEUITY 29 



On the contrary, among the nearest relatives of twins born from 

 one ovum twin-births occur in a ratio of 1 : 88. Compared with the 

 number of twin-births among the rest of the population, the ratio 

 of which is 1 : 92, no proof can be shown to be established, as Weinberg 

 points out, as to the inheritance of the power of giving birth to twins 

 from a single ovum. 



However, as one does not know, and with the method employed 

 cannot know, how many of these twin-births among the nearest relative 

 of the mothers giving birth to twins from one ovum are at the same time 

 one-egg births, one ought not to attach too great value to the above 

 figures as proof against the possibility of the hereditary nature of one- 

 egg twin-births. 



Let us assume that all these twins, born by the relatives of mothers 

 of one-egg twins, also were produced from one ovum. As it is shown 

 that among the births in the whole population twins born from one 

 ovum occur in the ratio of about 1 : 300 (according to the differentiation 

 method) the ratio 1 : 88 among the relatives would represent three 

 times the number characteristic of the rest of the population. There 

 is in such a case good reason to believe that the capacity of giving 

 birth to twins from one ovum is inherited. 



Thus granted that 60 per cent of the twins born by the mother's 

 relatives are produced from one ovum the frequency of one-egg twins 

 among the relatives of the mothers of one-egg twins is twice that of the 

 whole population. 



Weinberg now frankly assumes that 30 per cent (i. e. the same 

 percentage found in the whole population) of the twins belonging to 

 the nearest relatives of the mothers of one-egg twins also were pro- 

 duced from one ovum. 



Weinbeug also assumes that the mothers giving birth to twins 

 of different sexes from two ova not only are equal to the number of 

 mothers giving birth to twins of the same sex from two ova (= the hypo- 

 thesis of the differentiation method: see above) but that both these 

 categories of mothers also have an equal number of relatives and, 

 further, that these relatives have an equal number of children, and, 

 finally, that among these children the same percentage of twins are 

 to be found. 



The final figures, 64 pairs of twins (in 21 cases from one ovum!i 

 in 5645 births among the relatives of mothers who have given birth 

 to twins from one ovum, rest, therefore, upon a great many assump- 

 tions, which are more or less hypothetical. It is evident that such 



