Table C 11 by Weinberg: +Hereditary of the disposition to beget twins+ (Archiv für Rassen & Gesellschafts Biologie VI. 1909) is remarkable. "The difference in favour of sisters speaks for Mendel's law of dominance and recessivity. The more twins a woman has borne, the more frequently the same phenomena is found in her nearest female relations." That the mortality among twins is very great is a well-known fact.
About 2,000 families from Würtemberg family registers (after Weinberg).
In every 100,000 Births Twin Births occur in the following numbers:
Among daughters 1394 of mothers " maidens 1523 of twins " sisters 2135
In every 1,000 Births there are the following numbers of Twin Births among the immediate relatives:
Of all mothers 11 Of women who have had 1 multiple birth 17 " " 2 " " 20 " " 3 or more " 56
Percentage of deaths before the age of 20: Single-born Children 39 Twins 61
Figure C 12 the celebrated pedigree of the Hæmophilic +family+ (bleeders) +Mampel+ (by Rüdin after Lossen).
Figure C 13 showing the inheritance of progressive muscular +atrophy+ (after Eichhorst).
Figure C 14 a partial reproduction of a +pedigree+ comprising over 2,000 people of the family Nongaret suffering from inherited stationary night +blindness+ (compiled by Cunier, Truc and Nettleship). With regard to these figures it is to be noted that only a fraction of the offspring is affected with the illness, the remainder being perfectly normal. It is remarkable with the bleeders (Hæmophilic persons) that the females do not suffer from the disease though they transfer it to their male offspring; a similar latent disposition is observable in other hereditary conditions, especially colour-blindness.
W. Weinberg shows in Table C 15 the +frequency of tuberculosis within families+. He adds: "This is a comparison of the experiences of married tubercular individuals, regarding the frequency of tuberculosis among their parents, brothers and sisters, with the corresponding experiences of their husbands or wives who come on an average from similar surroundings. The experiences of the latter represent the normal expectation. It is especially striking that the family influence tells most with the children of the well-to-do." The well-known fact that the tuberculous frequently come from tuberculous stock is clearly demonstrated in the figures of this table.