172 THE BIOLOGY OF TWINS 



although they show differences in the presence of 

 certain friction-ridge patterns. It is interesting to 

 note the doubt in Wilder's mind as to the nature of 

 these twins. 



Of set VII, he says: 



This case has caused me considerable trouble, owing to a 

 preconceived notion that the marks ought to be found identical. 

 The family emphasized the facial resemblance of these twins, and 

 when I iirst saw them they certainly looked alike. One was, 

 however, an inch taller than the other, and the facial resemblance 

 after a short acquaintance did not seem as great. Upon unpre- 

 judiced comparison the prints of the palms are very different, 

 and not at all as in the case of true duplicates. The finger pat- 

 terns also do not at all correspond. The sole markings are similar 

 but not identical. The case is plainly one of fraternal twins that 

 resemble one another somewhat more than the average. 



In this connection let us recall, for a moment, the 

 case of the conjoined twins, Margaret and Mary, de- 

 scribed by Wilder in a later paper. In that case the 

 palm-prints were nearly identical, but the right sole of 

 Mary was totally different from her left and from either 

 sole of Margaret. If the criteria employed for set VII 

 were apphed to them, the twins Margaret and Mary 

 would be excluded from the category of dupHcates; yet 

 there can be no question as to their monozygotic origin. 



It must be emphasized also that a difference of one 

 inch in height in fifteen-year-old girls cannot be con- 

 sidered as evidence of dizygotic origin; in armadillo 

 quadruplets there are frequently much greater discrep- 

 ancies in size than this. It should furthermore not be 

 forgotten that the sole markings are similar in this 

 pair (Wilder's VII) and would doubtless have caused 



