I 82 



HEREDITY AND EUGENICS 



time in contact) considerably earlier in development 

 than do armadillo quadruplets. Indeed, the amount 

 of mirror-imaging is so small in human duplicate twins 

 that it appears probable that the separation (actually 

 of cells or ph3^siologically of nuclear elements) takes 

 place early in the cleavage, though not necessarily 



Fig. 30. — ^TwiN American Sailors of Irish Birth. 



at the first cleavage of the egg, as was formerly 

 supposed. It should be pointed out that this line of 

 reasoning, while attractive, is not necessarily con- 

 clusive according to the present state of our know- 

 ledge. 



A typical case of finger-print patterns in duplicate 



