Chap. 19 DEVELOPMENT 387 



arated. Quadruplets and quintuplets may include fraternals and identicals; the 

 odd one in quintuplets is usually regarded as a twin whose mate did not live 

 long. 



In man, apes and many- other mammals, only one infant is usually produced 

 at a time. According to estimates from statistics once in every 80 human 

 births, two are born at the same time, and triplets once in 512,000. Only 

 about 30 quintuplets have been recorded, and there are three substantiated 

 cases of the birth of sextuplets. At this date the famous Dionne quintuplets 

 of Canada and a similar series born in Argentina are the only groups of five 

 known to have survived. 



