144 



THE BIOLOGY OF TWINS 



from the left margin. It will be noted that, while both 

 fetuses of this pair are bilaterally symmetrical in the 

 anomaly, fetus I has complete doubling and fetus II has 

 incomplete doubhng. Fetuses III and IV have absolutely 

 identical bilateral doubling, but are asymmetrical in that 

 the left side of each has the type of doubling in every 

 detail of II, while the right side of each is completely 

 double like the condition in fetus I. 



These cases of band doubling must serve as samples 

 in that they show practically all the pecuKarities involved 



Fig. 46. — Diagrammatic representation of doublings in set A loi • 



in band doubling except those in which only one, two, 

 or three of the fetuses in the set show a doubling. One 

 case of that sort must be cited. 



Set A loi (male fetuses) is a case in which one pair 

 has band doubhng and the other has no doubhng at all 

 (Fig. 46). Fetus I has an exact bilaterally symmetrical 

 anomaly of band i, involving three double regions, two 

 lateral ones of nine scutes each, six scutes from the 

 margins, and a median doubhng of seventeen scutes. 

 Fetus II has the band double except six scutes on 

 the left margin. We must consequently inquire why 



