1 64 THE BIOLOGY OF TWINS 



Much more study is needed before this type of evidence 

 could be used as a rehable method of estabhshing rela- 

 tionships in man. 



Nevertheless, it is significant that peculiar patterns 

 in palm- and sole-prints are heritable just as are peculiar 

 patterns in the bands of armor in the armadillo. The 

 various modifications^ of the inherited pattern are also 

 like the various expressions of doubling in armadillo 

 scutes and bands. The patterns may be reproduced in 

 a more pronounced or in a reduced condition, but they 

 appear to be inherited in the expected proportions on 

 the basis of their unit character nature. Unfortunately 

 scarcely any information has been secured as to the 

 direct inheritance of palm and sole patterns. This 

 field would be well worth investigation. 



In concluding the discussion of the friction-ridge 

 correspondences it will be of interest to describe a 

 case worked out for a pair of "conjoined" twins (pygo- 

 pagi) by Wilder. These twin girls (Margaret and 

 Mary) were first observed a day or two after birth and 

 are now over four years old. ''They are united in the 

 sacro-iliac region, but are placed somewhat obliquely, 

 so that instead of looking in opposite directions they 

 are rotated about 45 degrees toward the same side." 

 A study of their palms and soles was deemed of great 

 interest, since there appeared to be no question as to their 

 monozygotic derivation. The palms of all four hands 

 are practically alike in pattern; the right hand of each 

 one not only mirrors its own left hand but also the 

 left hand of its twin partner. Since there is no asym- 

 metry in the hands, there is no chance to observe 

 symmetry reversal or mirror-imaging. Strange to say, 



