AS TO THE HEREDITY OF ACQUIRED CONDITIONS. 455 



by Goelilert * are of interest in this connection. He first gives a 

 table, from amongst the cases which he has collected, of the pairs 

 and sexes : — 



In examining this table it must, of course, be remembered that 

 the first two lines need not necessarily relate solely to homologous 

 twins. It is quite as possible for two children, of the same sex, 

 yet not true twins, to be born at a birth, as it is for two of 

 different sexes. Passing to tlie subject of heredity in twinning, 

 Goehlert states that there is a direct heredity from twin to twin 

 as well as an indirect. That this is not more observable is, he 

 remarks, due to the fact that so many twins die in childhood, 

 only seldom reaching maturity, and, of course, then not always 

 bearing children. He believes that in 132 of 192 cases selected 

 from Eoyal pedigrees which he carefully examined, the influence 

 of heredity was to be observed. The figures are given in the 

 subjoined table : 



From Father. From Mother. Pairs. 



Direct inheritance 5 11 16 



Indirect „ 57 55 112 



Direct and indirect . . 4 



62 66 132 



All that can be said is, that it is at least highly probable that 

 the production of true twins is hereditary. 



I have statedthat twins are not usually regarded as abnormalities; 

 yet the two are much more closely related than is generally thought. 

 Dr. Mitchell t shows this clearly in a paper, the conclusions drawn 

 in which are : — (1) Among imbeciles and idiots a much larger 

 proportion is actually found to be twin-born than among the 

 general community. (2) Among the relatives of imbeciles and 



* " Die Zwillinge," Virchow's Archiv, .Bd. 76, S. 457. 

 t Med. Times & Gaz. Nov. 15, 1862. 



