VARIATION AND HEREDITY IN TWINS 143 



and III and IV (a pair) are both bilateral. Perhaps 

 the most striking feature illustrated by this set is the 

 great variation in the extent of doubhng that may 

 appear in the four fetuses of a single set where there 

 can be no question as to the common genetic basis 

 of the more and of the less extensive expression of the 

 character. 



// 



Fig. 45. — Diagram of band doubling in set A 64 



By way of contrast, however, we shall present a case 

 in which the mother showed no doubling, but in which 

 the fetuses show a remarkable degree of resemblance 

 in the position and extent of the anomaly. Presumably 

 the condition has been inherited from the father. Fig. 45 

 is a diagrammatic representation of the doubling of bands 

 in Set A 64. Fetus I has the entire first band double, 

 for there are ten bands. Fetus II has a beautifully sym- 

 metric bilateral doubling of band i, consisting of fifteen 

 double scutes situated three places from the right and 



