THE LIMITS OF HEREDITY 197 



certain cows. Gynecological literature abounds with 

 cases of blighted twins, or of single births accom- 

 panied by an undeveloped foetus. Probably the 

 presence of lethal factors in some of the germ cells 

 accounts for many such cases. We have already 

 seen (p. 90) that brach3^dactyh' is perhaps lethal in 

 its effects w^hen present in the homozygous condition, 

 and the same is probably true of various other 

 abnormalities. Ihe conception of lethal factors is 

 thus destined to play an important part in the ex- 

 planation of many phenomena of reproduction in 

 man, and to furnish an explanation of sterility in some 

 cases where there has been no voluntary prevention 

 of children. 



A remarkable instance of a strain producing multiple 

 births has recenth^ been described (Davenport, 191 9). 

 A woman living in Cleveland, Ohio, has in three 

 successive marriages never had a single child at a 

 birth. She was born in Paris, and her mother and 

 her mother's mother are both said to have had only 

 twins, triplets, or quadruplets. By her first husband 

 she had twins. When he died she married a French- 

 Canadian, and bore twins, a boy and a girl. The girl 

 married and bore first a single child, and then twins, 

 who died with the mother shortly after birth. The 

 original mother next bore triplets ? ? c^ who died young. 

 Two years later twins ? S were born, and again the 

 following year twins ? S • By a third husband of 

 English and Scotch descent she had twins S c^ , who 

 died young, then triplets c^ ? ? , a boy still living and 

 two others born dead. This was followed by a 

 miscarriage of triplets ^ ? 5 , then twins ? c^ , the girl 

 dying shortly after birth. Next followed a mis- 

 carriage of quadruplets (^ c? ? ? , caused by poor health 

 of the mother. Twins ^ ? followed, the girl dying in 

 ten days, then triplets were born c? ? ? , the boy sur- 

 viving. In 1912 quadruplets, girls, were born; the 



